French President Nicolas Sarkozy and his U.S. counterpart Barack Obama on Thursday agreed to step up efforts to help end violence in Syria during a video conference, the Elysee Palace announced in a statement.

They also called on Iran to suspend sensitive atomic activities.

The two leaders urged Damascus "to scrupulously and unconditionally respect its undertakings in regard to the plan by the U.N. special envoy and the Arab League," warning that "the regime could be judged by its actions."

The two presidents, "in liaison with their partners, especially the Arab partners," agreed to intensify their efforts, including at the U.N. Security Council, to bring a definite end to the brutal repression against the Syrian people, the statement said.

They also pledged to find ways to deliver urgent humanitarian aids to the Syrian people in need, it said.

As for Iran, both Sarkozy and Obama "showed their determination to apply sanctions with the strongest firmness as long as Tehran refuses to comply with its international obligations, in particular Security Council resolutions on its military nuclear program," said the statement.

The two leaders "urged Iran to seize the opportunity to resume dialogue with the Six to engage in serious negotiations and suspend all sensitive nuclear activities," said the French presidency.

A new round of negotiations on the nuclear issue between Iran and the five permanent members of U.N. Security plus Germany (P5 +1) will be held on April 14 in Istanbul, Turkey.