The Syrian army and rebels sent reinforcements to Aleppo on Wednesday to join the intensifying battle for the country’s second city, as the United Nations pulled out half of its troubled observer mission. UN peacekeeping chief Herve Ladsous said he had told Syrian officials that without a significant reduction in violence, the remaining 150 observers would leave on the expiry of the “final” 30-day extension of the mission’s mandate agreed by the Security Council on July 20. Russia, meanwhile, ramped up its criticism of Western policy as helicopter gunships strafed several neighbourhoods of the commercial capital, causing deaths and injuries, the Syrian Observatory for Human Rights said. Nationwide at least 45 people were killed on Wednesday, most of them civilians, after 158 people died on Tuesday, the watchdog said. Rights group Amnesty International, meanwhile, warned on Wednesday about disturbing reports of “summary executions” by both Syrian troops and rebels, calling them “serious violations of international law.” Turkey said it was closing its border crossings with Syria until further notice after rebels seized two frontier posts. “We have taken such a measure for our citizens for security reasons,” a Turkish official said. “This is an open-ended measure and the reopening depends on the developments on the ground.” Russian Foreign Minister Sergei Lavrov lashed out at the United States for backing the armed opposition, saying a US failure to condemn the July 18 bombing that killed four top Syrian security officials meant it was justifying terror. “This is quite an awful position. I cannot even find the words to make clear how we feel,” Lavrov told reporters. “This is directly justifying terrorism. How can this be understood?” And a Russian foreign ministry statement said a new round of EU sanctions agreed this week, which allows for the inspection of vessels and planes suspected of carrying arms, amounted to an air and sea “blockade.” “Essentially, the measures taken by the European Union can be considered a declaration of a sea and air blockade of Syria,” the ministry said. It said experts needed to look into the EU legislation to see whether it was in line with international law. Clashes raged in Aleppo’s central Al Jamaliya neighbourhood, near the local headquarters of the ruling Baath party. In Kalasseh in the south, rebels set fire to a police station, the Observatory said. War planes overflew the city, breaking the sound barrier but not opening fire, Observatory director Rami Abdel Rahman said. He also said the rebels “are sending numerous fighters to Aleppo to battle the regime because, for them, Aleppo is as important as Benghazi was for the Libyan rebels.” “Aleppo is the capital of the north and the northern regions are already in their hands so, if this city falls, the regime is over and the two sides know it.” A rebel spokesman said via Skype that a “large number” of troops have been moved from the northwestern province of Idlib to Aleppo. Free Syrian Army Colonel Abdel Jabbar Al Oqaidi said he believed the reinforcements were being sent because of the intensity of clashes in Aleppo, where several districts were “liberated” on Monday. “There are clashes right now in Aleppo, so fierce that many of their troops are running away, while dozens of others are defecting on the spot,” Oqaidi said. “Their morale is very low.” A Syrian newspaper journalist confirmed the rebels were also reinforcing. “Hundreds of rebels from all over the north of Syria are arriving in Aleppo, which appears to have become the decisive battle,” the journalist said. The Britain-based Observatory also reported clashes in the Al Hajar Al Aswad district of Damascus, one of the last remaining rebel bastions after 10 days of fighting there. Helicopter gunships and heavy machinegun fire pounded the embattled southern neighbourhood, the Observatory said. In Hama province in central Syria, a couple and their two children were killed as they tried to flee shelling. A video distributed by the Observatory showed grisly footage of the bodies.