BEIRUT (AP) -- Russian President Vladimir Putin on Saturday questioned the U.S. commitment to a shaky cease-fire in Syria, suggesting that Washington wasn't prepared to break with "terrorist elements" battling Syrian President Bashar Assad's forces.
The truce has largely held since going into effect on Monday, but both sides have alleged dozens of violations, and aid convoys have been unable to enter rebel-held parts of the northern city of Aleppo -- a key opposition demand.
Russia has in turn accused Washington of failing to rein in the rebels, and on Saturday Putin asked why the United States has insisted on not releasing a written copy of the agreement. Officials have provided details of the agreement in press conferences, but have not released an official document, fueling suspicions on both sides.
"This comes from the problems the U.S. is facing on the Syrian track - they still cannot separate the so-called healthy part of the opposition from the half-criminal and terrorist elements," Putin said during a trip to Kyrgyzstan.
"In my opinion, this comes from the desire to keep the combat potential in fighting the legitimate government of Bashar Assad. But this is a very dangerous route."
He appeared to be referring to the Fatah al-Sham Front, an al-Qaida-linked group previously known as the Nusra Front, which is deeply embedded in rebel-held areas and fights alongside more moderate groups.
Russian Foreign Minister Sergey Lavrov echoed Putin's remarks during a phone call with U.S. Secretary of State John Kerry. Lavrov noted the "refusal by an array of illegal armed groups to join the cease-fire," and Washington's obligation to "separate units of the moderate opposition from terrorist groupings," according to a Foreign Ministry statement.
Under the cease-fire agreement, the U.S. and Russia would work together to target the Fatah al-Sham Front, as well as the Islamic State group, while Assad's forces refrain from striking opposition-held areas.
But Washington has warned Russia that unless aid is delivered to Aleppo, it will not move ahead with the formation of the joint coordination center.
The U.N. has accused Assad's government of obstructing aid access to the contested city. The Russian military says insurgents have held up the delivery by firing on government positions along the main route leading into besieged, rebel-held districts, in violation of the cease-fire.
The Syrian government said it has done all that is necessary to facilitate the entry of aid convoys to Aleppo, but that armed groups have failed to withdraw from the supply routes and are committing "dangerous, provocative acts."
Russia's military said Syrian rebels violated the cease-fire dozens of times over the past day, including with strikes on military and civilian targets in Aleppo.
The Interfax news agency quoted Col. Sergei Kopytsin as saying Saturday that mortar fire and homemade rockets struck Aleppo 26 times. Russian news agencies cited another official, Lt. Gen. Vladimir Savchenko, as saying there had been 55 violations throughout the country. Syria's state news agency SANA said insurgents have violated the cease-fire 12 times in the last 12 hours. No casualties were reported.
Syrian activists said government forces have meanwhile killed five civilians. The Britain-based Syrian Observatory for Human Rights said a woman and child were killed Saturday in Talbiseh, in the central Homs province. It says two men were killed outside Damascus and a child was killed in Aleppo province.
The Syrian Civil Defense group in Homs said government artillery caused the deaths in Talbiseh. A video of the rescue mission showed bodies strewn across the ground.
Syria's conflict has killed more than 300,000 people and displaced half the country's population since March 2011.