WASHINGTON

The U.S. said Tuesday its "first and foremost" focus with Russia is to discuss sustainable proposals for the cease-fire to hold in Syria, while Moscow says it is ready for joint operations against Daesh or al-Nusra.

"What we're discussing right now with Russia are proposals for a sustainable mechanism that helps support that and strengthen that cessation of hostilities," in Aleppo and Damascus, U.S. State Department spokesman Mark Toner told reporters.

However, he added that the U.S. continues to work and support the efforts of the Syrian Democratic Forces (SDF) "to retake territory from Daesh" and its other efforts to defeat the group.

The SDF is an alliance predominantly consisting of the Kurdish PYD, a Syrian offshoot of the PKK terrorist group.

The “cessation of hostilities” agreement was reached by the U.S. and Russia in February in a bid to de-escalate the five-year conflict and pave the way for peace talks in Geneva between the regime and opposition.

Toner's comments came after Russian Foreign Minister Sergey Lavrov said earlier Tuesday in Uzbekistan that Russia is ready to coordinate efforts with the U.S.-led coalition and Kurdish groups in Syria.

"I cannot say how real reports are that such actions have already begun, but we are ready for such coordination," Lavrov said.

Meanwhile, U.S. Central Command confirmed that the operation is led by the SDF.

“We have always been focused on Raqqa and evicting Da’esh from the self-declared capitol of their so-called ‘caliphate’,” CENTCOM wrote to Anadolu Agency in an email.

"We will provide support to our partners’ operations as we have previously."

The Raqqa offensive focuses on the northern outskirts of the city, according to a Syrian Democratic Force Commander who was quoted on the group’s Twitter account.

The operation on Raqqa comes just after Central Command Commander Gen. Joseph Votel secretly visited Syria and met leaders of local fighters in northeastern parts of the war-torn country.

The offensive also came as Iraqi forces are encircling Mosul, Iraq’s second-largest city, which fell to Daesh in 2014, a move that seems to put pressure on Raqqa to lessen Daesh’s energy in Mosul.

Last week, Russia said it made a proposal to U.S. for it and the U.S. to conduct joint airstrikes against Daesh and al-Nusra beginning on May 25.

However, the Pentagon said it had not been formally notified of a Russian proposal for a joint action.