WASHINGTON (Reuters) - Russia has said it is willing to deploy monitors to prevent any violations of a ceasefire in southwestern Syria by Syrian government forces, a senior U.S. official said on Thursday.

FILE PHOTO: Brett McGurk, U.S. envoy to the coalition against Islamic State, speaks during news conference at the U.S. Embassy in Baghdad, Iraq July 8, 2017. U.S. Embassy/Handout via REUTERS

Brett McGurk, U.S. special envoy for the coalition against Islamic State, said the United States was “very encouraged” by the progress since the ceasefire arranged by the United States, Russia and Jordan took effect on Sunday.

“The Russians have made clear they’re very serious about this and willing to put some of their people on the ground to help monitor from the regime side,” McGurk told reporters. “They do not want the regime violating the ceasefire.”

Russia is the main backer of Syrian President Bashar al-Assad, and Russian air power and Iranian-backed militias have helped put mostly Sunni rebels at a disadvantage over the past year.

The wide array of rebels fighting Assad since 2011 includes jihadist factions and other groups supported by the United States, Turkey and Gulf monarchies.

The “de-escalation agreement” for southwestern Syria was announced after a meeting between U.S. President Donald Trump and Russian President Vladimir Putin in Germany on Friday.

Trump, in a news conference in Paris on Thursday, said work was under way to negotiate a ceasefire in a second region of Syria.

“I think the president is referring to a very constructive discussion that he had with the Russians in building from this southwest agreement,” McGurk said when asked about Turmp’s remark.

The United States has had “very constructive ... military-to-military discussions with the Russians about deconfliction arrangements” in recent weeks and is keen to explore the possibility of ceasefires in other areas, he said.

McGurk said the United States, Russia and Jordan had conducted extensive discussions to agree on a detailed line of contact as a basis for the southwestern ceasefire, and were now looking at where monitors could be placed.

“That discussion is very much ongoing, and I’m hopeful over the next week or so it can get somewhere,” he said.

Earlier on Thursday at a meeting of the anti-IS coalition in Washington, McGurk said Washington had pledged an additional $119 million for humanitarian aid in Iraq following the recapture of Mosul from Islamic State this month.

He urged efforts and funds to stabilize areas of Iraq and Syria where allied forces had defeated the militants.

“We have identified 100 critical stabilization sites in and around Mosul which will be the immediate focus for de-mining and restoration,” McGurk said at the beginning of Thursday meeting.

Iraqi forces clashed with Islamic State fighters holding out in Mosul’s Old City on Wednesday, more than 36 hours after Baghdad announced victory over the jihadists in what the militant group had declared the de facto Iraqi capital of its “caliphate.”

Iraqi Prime Minister Haider al-Abadi’s victory announcement signaled the biggest defeat for the hard-line Sunni group since its lightning sweep through northern Iraq three years ago. But pockets of Mosul remain insecure and the city has been heavily damaged by nearly nine months of grueling urban combat.