BEIRUT/MOSCOW: Russia and Syrian rebels cast doubt over the prospects for an increasingly shaky five-day-old ceasefire on Saturday, with Moscow saying the situation was worsening and a senior insurgent warning that the truce 'will not hold out'. The ceasefire is the result of an agreement between Russia, which backs Syrian President Bashar al-Assad with air power, and the United States, which supports some rebel groups, and has cooled fighting since coming into effect on Monday. However, some violence has persisted across Syria, and promised aid deliveries to besieged areas remain blocked, with both sides accusing the other of bad faith. Russia's Defence Ministry said conditions in Syria were deteriorating, adding that it believed the ceasefire had been breached 199 times by rebels and saying the United States would be responsible if it were to collapse. Earlier on Saturday, Russian President Vladimir Putin cast doubt over Washington's commitment to the deal, but also said he believed that securing a ceasefire was a common goal for the two countries, which both agreed to extend it on Friday. Insurgents say they only reluctantly accepted the initial deal, which they believe is skewed against them, because it could relieve the dire humanitarian situation in besieged areas they control, and blamed Russia for undermining the truce. 'The truce, as we have warned, and we told the (US) State Department - will not hold out,' the rebel official said, pointing to the continued presence of a UN aid convoy at the Turkish border awaiting permission to travel to Aleppo. 'It is not possible for the party (Russia) that wages war against a people to strive to achieve a truce, as it is also not possible for it to be a sponsor of this agreement while it bombs night and day, while on the other side, the other party - America - has the role of spectator,' he said. Moscow has itself accused rebels of breaking the truce and said Washington needs to do more to make them abide by its terms, including separating from the jihadist Jabhat Fateh al-Sham, which only broke formal allegiance to al Qaeda in July. The five-year-old civil war has killed hundreds of thousands and displaced half the country's population, drawing in global and regional powers, causing an international refugee crisis and inspiring jihadist attacks around the world. Overnight Shelling Both sides have accused the other of being responsible for aid deliveries being stuck far from Aleppo, where army and rebel forces were supposed to pull back from the Castello Road which leads into besieged, insurgent-held eastern districts. Russia on Friday said the Syrian army had initially withdrawn but returned to its positions after being fired on by rebels, who in turn say they saw no sign of government forces ever leaving their positions. 'There is no change,' said Zakariya Malahifji, an official for a rebel group in Aleppo on Saturday, asked whether there had been any move by the army to withdraw from positions along the road. The United Nations said the government was holding up aid by denying letters guaranteeing access. Warplanes strafed or bombed rebel-held areas in the northwestern province of Idlib, as well as positions north of the city of Homs and east of the city of Hama overnight, the Syrian Observatory for Human Rights said. The Britain-based war monitoring group also reported clashes between the army and rebels or shelling overnight in the capital's Eastern Ghouta suburbs, in Ramousah south of Aleppo and in the southern province of Deraa. Islamic State Turkey-backed Free Syrian Army rebels are pushing south in northern Syria from the towns of al-Rai and Azaz towards the Islamic State-held town of al-Bab, supported by tanks and jets, security sources said, clashing with the jihadist group. Vehicles were mobilised in northern Syria across from the Turkish village of Arapakesmez from the early hours of the morning and Turkish artillery deployed at the border have fired at Islamic State targets. CNN Turk footage showed white smoke rising from across the border in Syria as Turkish howitzers fired west of al-Rai, where some US special forces briefly deployed to help coordinate air strikes against the militants before withdrawing on Friday. If the ceasefire deal is successful, Moscow and Washington will start to share targeting information on militant groups, including Islamic State, they have said.