Russian military police forces are seen at the Wafideen area near the town of Douma, on the northeast of Damascus, Syria, on April 12, 2018. (Xinhua/Monsef Memeri)

MOSCOW, April 12 (Xinhua) -- Russian President Vladimir Putin and his Turkish counterpart Recep Tayyip Erdogan voiced concern over developments in and around Syria during a phone conversation Thursday, the Kremlin said.

The two presidents stressed the importance of ensuring necessary conditions for the work of the Organization for the Prohibition of Chemical Weapons mission sent to Syria to investigate an alleged chemical weapon attack, it said.

"Both leaders spoke in favor of stepping up the political settlement process in Syria based on UN Security Council Resolution 2254 and the decisions made by the (Syrian) National Dialogue Congress in Sochi," the Kremlin said.

On Saturday, rebels in the formerly rebel-held Douma district of Damascus accused the Syrian forces of using chlorine gas, which led to the death of 40 people.

The Syrian government totally denied the claims, saying the rebels were fabricating incidents to attract foreign strikes on Syria.

U.S. President Donald Trump on Wednesday threated to launch a missile attack on Syria over the alleged chemical weapon attack, but he tweeted Thursday that the attack "could be very soon or not so soon at all!"

Russian Foreign Ministry spokesperson Maria Zakharova said at a news briefing Thursday that the threat to use force against a UN member state is a "blatant violation of the UN Charter."