Washington — The United States warned Russia on Friday that potential military cooperation envisioned by a ceasefire deal in Syria will not happen unless humanitarian aid begins to flow into Aleppo and other besieged communities.Secretary of State John Kerry told Russian Foreign Minister Sergey Lavrov in a telephone call that Moscow must persuade the Syrian government to get the aid moving or a joint facility to coordinate attacks on extremist groups and share intelligence will not be set up, the State Department said. Kerry called the delays in assistance to Aleppo "repeated" and "unacceptable" and said Russia must press Syrian President Bashar Assad to allow deliveries.Kerry "emphasised that the United States expects Russia to use its influence on the Assad regime to allow UN humanitarian convoys to reach Aleppo and other areas in need," State Department spokesperson John Kirby said. "The secretary made clear that the United States will not establish the Joint Implementation Center with Russia unless and until the agreed terms for humanitarian access are met."The agreement that Kerry and Lavrov reached last week calls for sustained delivery of humanitarian aid, along with a decrease in violence, as a requirement for the military cooperation to target Islamic State and al-Qaeda-linked groups. The arrangements are very detailed on the mechanics of ending violence in Aleppo and opening up a key artery to the city for humanitarian deliveries. The agreement has not been made public but officials familiar with it have said it contains a highly technical series of requirements for both Assad's government and opposition forces.These include precise calculations, in meters, on how the sides would pull back from a key artery into Aleppo and where they would have to redeploy weaponry. A main focus is on ensuring rapid, safe, unhindered and sustained humanitarian access to all people in need.The Russian Foreign Ministry's description of the call said the two men had focused on implementation of the agreement, according to Russian news agencies.The ministry said Lavrov had once again called for the United States to make the agreement public and have the United Nations Security Council endorse it. He also restated Moscow's demand that the US use its influence with opposition forces it supports to distance themselves from al-Qaeda-linked fighters.Meanwhile, a senior Russian military official said Moscow would help ensure the cease-fire in Syria for another three days, but warned the United States to press the rebels to end violations of the truce.Lieutenant General Viktor Poznikhir of the Russian military's General Staff declared readiness to extend the US-Russia-brokered cease-fire for another 72 hours, adding that Moscow expects Washington to take "resolute action" to end violations by the US-backed opposition units. He said the Syrian army has fully complied with the truce that went into force on Monday, while the opposition units have violated it 144 times since then.