LE BOURGET, France — President Obama urged Russian President Vladimir Putin on Monday to decrease tensions with Turkey, as the U.S. and Russian leaders met briefly on the sidelines of global climate talks outside Paris.

During the 30-minute sit-down, Obama expressed regret over Turkey’s downing of a Russian plane that Turkey said had entered its airspace from Syria, said Putin spokesman Dmitry Peskov. He said the two leaders discussed Syria in detail, and they both spoke in favor of moving toward the launch of a political settlement to Syria’s civil war.

Russia and the U.S. are both involved in a new diplomatic effort in Vienna to bring about a ceasefire, potentially within weeks.

The White House said that Obama told Putin that Syrian President Bashar Assad must leave power as part of that transition, a long-held U.S. position that remains at odds with Russia’s support for Assad. Obama also called on Russia to focus its airstrikes in Syria on Islamic State militants, not rebels fighting Assad, the White House said.

The two leaders also discussed implementing a ceasefire in Ukraine.