U.S. President Barack Obama and French President Nicolas Sarkozy called on Syria to abide fully with a UN-backed plan to stop a "brutal crackdown" and vowed to intensify efforts to end the violence, including steps at the UN Security Council.
In a statement issued after a conference call between the two men, the leaders also urged Iran to undertake serious negotiations when major powers begin talks with the Islamic Republic in Istanbul on Friday.
"The two presidents urged the Syrian regime to respect scrupulously and without preconditions its commitments to the plan of the Arab League-UN envoy. The regime will be judged by its acts," the statement said.
UN-Arab League envoy Kofi Annan told the Security Council on Thursday that Syria has not fully complied with the terms of his peace plan and urged the 15-nation body to demand the withdrawal of troops and heavy weapons from towns, council diplomats said.
Paris previously has said it would go back to the Security Council if Damascus failed to implement the six-point plan that includes a political transition.
"With their partners, notably Arabs, they (Sarkozy, Obama) agreed to intensify their efforts to finally end the brutal repression of the Syrian people so that an immediate humanitarian assistance can be given... Those who have committed acts of violence will have to answer to their crimes," the statement said.
The two leaders, who also discussed Afghanistan and the price of oil, said they would also apply sanctions on Iran for as long as Tehran did not meet its international obligations.
Major powers will hold their first talks with Iran on Friday in more than a year, hoping Tehran will give enough ground over its nuclear program to continue negotiations and avert the threat of a Middle East war.
"They called on Iran to use the occasion to ... undertake serious discussions and suspend all its sensitive nuclear activities," the statement said.
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