ASTANA, Kazakhstan — Iran, Russia and Turkey presented a united front at the conclusion of two days of talks in Kazakhstan between the Syrian government and the armed opposition, pledging support for the country's shaky cease-fire and a joint mechanism to ensure compliance.

They did not specify how that would work, and continued differences among the warring sides as well as rebel infighting back home threatened to scuttle the deal.

“It's going to be a challenge, it's not going to be easy,” Staffan de Mistura, the U.N.'s Syria envoy, who mediated between the two sides in the Kazakh capital of Astana, told reporters later.

Russia and Iran, President Bashar Assad's main supporters, and Turkey, the rebels' chief backer, said they will use their “influence” to strengthen the truce, which has been in place since Dec. 30. Their joint efforts have raised hopes for a diplomatic end to the nearly six-year conflict.

Previous efforts by the U.S. and Russia for a lasting cease-fire led nowhere.

U.S. State Department spokesman Mark Toner said Tuesday that the U.S. welcomes actions that de-escalate violence in the country and called on Russia, Iran and Syria to press the Syrian sides to abide by the cease-fire in order to create an environment more conductive to political discussions.

The U.S., busy with the presidential transition, had no significant role in the talks between the Syrian government and its armed opponents in Kazakhstan this week.

Following Tuesday's declaration, read out by Kazakhstan's foreign minister, Kairat Abdrakhmanov, Syria's delegates to the Astana meeting held competing news conferences that underlined the differences between the two sides.

“We don't accept any role for Iran in the future of Syria,” said Mohammad Alloush, head of the rebel delegation, insisting that all Iranian-backed foreign militias fighting alongside the Syrian government withdraw from Syria.

Syria's U.N. envoy Bashar Ja'afari, called it “pitiful” that the opposition was criticizing one of the three guarantors who facilitated the agreement.

“The issue here is that finally we have a consensual paper called final communique or final declaration agreed upon by everybody this is what we care about,” Ja'afari said.

Ja'afari, however, said that military operations in an area near the Syrian capital would continue despite a pledge to enforce the cease-fire “as long as there are terrorists depriving seven million people in the capital Damascus from drinking water.”

The government says al-Qaida-linked militants are present in Ain al-Fijeh, which is in the water-rich Barada Valley northeast of Damascus. Ja'afari accused insurgents of using the water as a weapon, but the rebels deny an al-Qaida-linked group is in the area, and have negotiated to include it in the cease-fire agreement.

On Tuesday, fighting broke out in northwestern Syria between Fatah al-Sham and one of the rebel factions present at the Astana talks, the Jaysh al-Mujahedeen. The infighting threatened to expand into wider battles, as other rebel groups rallied around Jaysh al-Mujahedeen.

De Mistura said Russia, Iran and Turkey would meet soon in Astana to lay the parameters for a mechanism to reinforce the truce.