Obama urges diplomatic push on Iran nuclear programme.
US President Barack Obama has said recent moves by Iran should offer the basis for a "meaningful agreement" on its nuclear programme.
Speaking at the UN General Assembly's annual meeting, Mr Obama said words now had to be "matched by actions that are transparent and verifiable".
The US leader recently exchanged letters with his newly-elected counterpart over the nuclear issue.
Mr Obama also called for a strong UN resolution on Syria's chemical arms.
He said the purpose of such a resolution should be "to verify that the [Bashar al-Assad's] regime is keeping its commitments" to remove or destroy its chemical weapons.
He said it was an "insult to human reason and to the legitimacy of this institution [the UN] to suggest that anyone other than the regime carried out" a sarin gas attack which UN inspectors have verified took place on 21 August.
Mr Obama referred to Iranian suffering from chemical weapons at the hands of Iraq when he said the ban on chemical weapons was "strengthened by the searing memories of soldiers suffocated in the trenches; Jews slaughtered in gas chambers; and Iranians poisoned in the many tens of thousands".
Analysis
Acknowledging the pain of the other can often be the first step towards some form of reconciliation.
For two countries that have had no diplomatic relations for three decades, Mr Obama's mention of the suffering of Iranians dying from sarin gas attacks in the waning years of the Iran-Iraq war is akin to an olive branch.
Mr Rouhani was not in the UN chambers but his foreign minister was.
The two countries are now engaged in an elaborate diplomatic dance, which will last all week. No-one expects a tangible breakthrough - years of difficult history cannot be overcome overnight, and it's hard to see how Washington and Tehran's regional interests will ever overlap.
But it's the first time since Obama made his offer to engage America's foes during his 2009 inaugural speech that Iran has responded so positively and so publicly.
The deal for Syria to hand over its chemical weapons by mid-2014 was agreed earlier this month between the US and Russia, averting a possible Western military strike.
Differences have since emerged over whether the deal should be enforced by a UN Security Council resolution under Chapter VII of the organisation's charter, which would authorise sanctions and the use of force if Syria did not comply with its obligations.
Opening the UN summit on Tuesday, Secretary-General Ban Ki-moon said the Syrian government must "fully and quickly honour" its obligations under the deal.
"The international community must bring to justice the perpetrators of the use of chemical weapons in Syria, confirmed unequivocally by the UN investigation mission," he said.
Handshake?
On Iran, Mr Obama said the US wanted to resolve the nuclear issue peacefully, but was determined to prevent Iran from developing a nuclear weapon.
"We are not seeking regime change, and we respect the right of the Iranian people to access peaceful nuclear energy," he insisted - an acknowledgment of the assertion frequently made by Iranian authorities.
"Instead, we insist that the Iranian government meet its responsibilities under the Nuclear Non-Proliferation Treaty and UN Security Council resolutions."
"The roadblocks may prove to be too great, but I firmly believe the diplomatic path must be tested" he added further into the speech, saying he had urged Secretary of State John Kerry to pursue a deal.
Iran insists it is a peaceful programme, but Western countries suspect it of seeking to develop a nuclear weapon.
The country's new President, Hassan Rouhani, has said he wants to present his country's "true face".
A meeting between Mr Obama and Mr Rouhani - the first such encounter since the 1979 revolution - has not been ruled out.
They are expected to be at the same lunch on Tuesday, and the White House has left the door open to the possibility of a handshake.
On Thursday, Iran's Foreign Minister Mohammad Javad Zarif will discuss its nuclear programme with Mr Kerry - a rare instance of a formal encounter between the counterparts, say correspondents.
A foreign ministry spokeswoman in Tehran said the meeting represented the "beginning for nuclear talks in the new era".
The meeting will be attended by foreign ministers from the other four permanent UN Security Council members - the UK, China, France and Russia - and also Germany, which make up the so-called P5+1.
Mr Rouhani has said he is ready to restart stalled nuclear talks without preconditions.
The UK welcomed statements from Iran that it wanted to improve relations with the West
Western ministers will want to see an Iranian willingness to make concessions on its nuclear programme if there is to be any lifting or lightening of UN and Western sanctions, BBC diplomatic correspondent Jonathan Marcus says.
Speaking at the UN General Assembly's annual meeting, Mr Obama said words now had to be "matched by actions that are transparent and verifiable".
The US leader recently exchanged letters with his newly-elected counterpart over the nuclear issue.
Mr Obama also called for a strong UN resolution on Syria's chemical arms.
He said the purpose of such a resolution should be "to verify that the [Bashar al-Assad's] regime is keeping its commitments" to remove or destroy its chemical weapons.
He said it was an "insult to human reason and to the legitimacy of this institution [the UN] to suggest that anyone other than the regime carried out" a sarin gas attack which UN inspectors have verified took place on 21 August.
Mr Obama referred to Iranian suffering from chemical weapons at the hands of Iraq when he said the ban on chemical weapons was "strengthened by the searing memories of soldiers suffocated in the trenches; Jews slaughtered in gas chambers; and Iranians poisoned in the many tens of thousands".
Analysis
Acknowledging the pain of the other can often be the first step towards some form of reconciliation.
For two countries that have had no diplomatic relations for three decades, Mr Obama's mention of the suffering of Iranians dying from sarin gas attacks in the waning years of the Iran-Iraq war is akin to an olive branch.
Mr Rouhani was not in the UN chambers but his foreign minister was.
The two countries are now engaged in an elaborate diplomatic dance, which will last all week. No-one expects a tangible breakthrough - years of difficult history cannot be overcome overnight, and it's hard to see how Washington and Tehran's regional interests will ever overlap.
But it's the first time since Obama made his offer to engage America's foes during his 2009 inaugural speech that Iran has responded so positively and so publicly.
The deal for Syria to hand over its chemical weapons by mid-2014 was agreed earlier this month between the US and Russia, averting a possible Western military strike.
Differences have since emerged over whether the deal should be enforced by a UN Security Council resolution under Chapter VII of the organisation's charter, which would authorise sanctions and the use of force if Syria did not comply with its obligations.
Opening the UN summit on Tuesday, Secretary-General Ban Ki-moon said the Syrian government must "fully and quickly honour" its obligations under the deal.
"The international community must bring to justice the perpetrators of the use of chemical weapons in Syria, confirmed unequivocally by the UN investigation mission," he said.
Handshake?
On Iran, Mr Obama said the US wanted to resolve the nuclear issue peacefully, but was determined to prevent Iran from developing a nuclear weapon.
"We are not seeking regime change, and we respect the right of the Iranian people to access peaceful nuclear energy," he insisted - an acknowledgment of the assertion frequently made by Iranian authorities.
"Instead, we insist that the Iranian government meet its responsibilities under the Nuclear Non-Proliferation Treaty and UN Security Council resolutions."
"The roadblocks may prove to be too great, but I firmly believe the diplomatic path must be tested" he added further into the speech, saying he had urged Secretary of State John Kerry to pursue a deal.
Iran insists it is a peaceful programme, but Western countries suspect it of seeking to develop a nuclear weapon.
The country's new President, Hassan Rouhani, has said he wants to present his country's "true face".
A meeting between Mr Obama and Mr Rouhani - the first such encounter since the 1979 revolution - has not been ruled out.
They are expected to be at the same lunch on Tuesday, and the White House has left the door open to the possibility of a handshake.
On Thursday, Iran's Foreign Minister Mohammad Javad Zarif will discuss its nuclear programme with Mr Kerry - a rare instance of a formal encounter between the counterparts, say correspondents.
A foreign ministry spokeswoman in Tehran said the meeting represented the "beginning for nuclear talks in the new era".
The meeting will be attended by foreign ministers from the other four permanent UN Security Council members - the UK, China, France and Russia - and also Germany, which make up the so-called P5+1.
Mr Rouhani has said he is ready to restart stalled nuclear talks without preconditions.
The UK welcomed statements from Iran that it wanted to improve relations with the West
Western ministers will want to see an Iranian willingness to make concessions on its nuclear programme if there is to be any lifting or lightening of UN and Western sanctions, BBC diplomatic correspondent Jonathan Marcus says.
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