Syria's Foreign Minister Walid al-Moallem speaks during a press conference held at the Foreign Ministry in Damascus, capital of Syria, May 8, 2017. Walid al-Moallem said Monday that his government will abide by the de-escalation zones' deal, warning, however, any breach by the rebels will be retaliated. (Xinhua/Ammar Safarjalani)

WASHINGTON, May 15 (Xinhua) -- The U.S. State Department said on Monday that the United States was skeptical of a new agreement signed by Russia, Turkey and Iran to reduce violence in certain areas of Syria.

"In light of the failures of the past cease-fire agreements, we have reason to be skeptical," said Stuart Jones, the acting assistant secretary for Near Eastern Affairs, here at a briefing, adding that Russia must bear responsibility to ensure compliance of the Syrian government.

"During his visit here last week, (Russian) Foreign Minister Lavrov acknowledged that there's no military solution to the Syrian conflict," he added.

The de-escalation zones deal went into effect in Syria at midnight Saturday, according to Syrian local media reports.

According to the agreement, the Syrian government and opposition forces will halt fighting for six months in four zones: the northwestern province of Idlib, the central province of Homs, the Eastern Ghouta countryside of Damascus and areas in the Daraa and Qunaitera provinces in southern Syria.

The U.S. State Department in an earlier statement also voiced concerns about Iran's role as a guarantor of the new memorandum to reduce violence in certain areas of Syria.

Also in the briefing on Monday, Jones accused the Syrian government of killing prisoners and burning the bodies in a crematorium outside the capital.

The allegation came less than a week before U.S. President Donald Trump's planned first foreign trip since taking office.