Syrian forces launched an all-out assault on opposition strongholds in Damascus Friday, a day after rebels seized crossings on the Iraq and Turkey borders on the 16-month conflict\'s deadliest day so far. Rebel fighters also clashed with troops in several neighbourhoods of Aleppo in what the Britain-based Syrian Observatory for Human Rights said was the fiercest fighting so far in Syria\'s second city. At the United Nations, the Security Council voted unanimously to give a \"final\" 30-day extension to a troubled observer mission that was charged with overseeing peace plan for Syria but which suspended its operations on June 16 in the face of mounting violence. The vote came after emergency consultations just hours before the expiry of the 300-strong mission\'s mandate after Russia threatened to use its veto powers as a council permanent member for the second time in as many days. At a closed meeting with top ministers, Russian President Vladimir Putin warned Western powers not to take action against the Syrian government outside the auspices of the Security Council, Russian news agencies reported. \"In the opinion of the Russian president, any attempts to act outside the UN Security Council will be ineffective and only undermine the authority of this international organisation,\" Kremlin spokesman Dmitry Peskov was quoted as saying. A security source said the military had launched a general offensive in the capital. \"Our brave army forces have completely cleansed the area of Midan in Damascus of the remaining mercenary terrorists and have re-established security,\" it said, using the regime term for rebels. Reporters taken on a regime-organised trip of Midan saw three bodies, empty streets, shuttered shops and buildings pockmarked with bullet holes. The assault comes after a Wednesday bombing that killed four senior members of the regime, including the national security chief, who died on Friday. General Hisham Ikhtiyar had been wounded along with Interior Minister Mohammed al-Shaar in the National Security headquarters bombing, which was claimed by the Free Syrian Army (FSA). Defence Minister General Daoud Rajha, President Bashar al-Assad\'s brother-in-law Assef Shawkat and General Hassan Turkmani, head of the regime\'s crisis cell on the uprising, were all killed in the explosion. A state funeral was held for the three in Damascus on Friday ahead of their burials in their native provinces, the official SANA news agency reported, adding that Vice President Faruq al-Shara had attended but not Assad himself. After Wednesday\'s bombing, a security source warned that the regime would step up its operations against the rebels. \"The army has so far exercised restraint in its operations, but after the attack, it has decided to use all the weapons in its possession to finish the terrorists off,\" the source said. A security source told AFP the army was now in control of the Damascus neighbourhoods of Midan, Tadamon, Qaboon and Barzeh, while fierce clashes were reported in other districts including Jubar, Mazzeh and Kfar Susa. The Observatory also reported intense fighting in several neighbourhoods of Aleppo and said troops opened fire on a large demonstration in the city, Syria\'s\'s commercial centre. It said 16 people were killed in Aleppo, 10 of them civilians. They were among 128 people dead nationwide, including 85 civilians, at least seven of them children. The deaths came after 302 people were killed on Thursday, according to the Observatory, making it the deadliest day of the uprising so far. Raging battle at border post Clashes took place even on Syria\'s frontiers, activists and witnesses said. An AFP photographer reported that FSA fighters fought a raging battle with Syrian troops at the Bab al-Hawa border post with Turkey and that some 150 rebels controlled the crossing on Friday. On Thursday, Iraq\'s deputy interior minister Adnan al-Assadi told AFP that the FSA had seized control of all three crossings along their common border. At the Albu Kamal border point, an AFP photographer saw a watchtower apparently empty and crossing buildings deserted. He reported that a poster of Assad had the head torn off, and that no flags were raised above the border point. At the United Nations, Security Council permanent members Russia and China both voted in favour of a British-drafted resolution extending the mandate of the UN Supervision Mission in Syria for a \"final\" 30 days, a day after blocking another text that could have imposed sanctions on the regime. Thursday\'s vetos sparked Western outrage but Russian ambassador Vitaly Churkin had threatened to use Moscow\'s veto again. Russia had wanted an unconditional extension of the mission for a renewable 45 days. The resolution adopted said the council only keep UNSMIS going after the 30 days if UN \"reports and the Security Council confirms the cessation of the use of heavy weapons and a reduction in the level of violence sufficient to allow UNSMIS to implement its mandate.\" Western envoys have stressed that they believe UNSMIS will now be closed down. UN chief Ban Ki-moon said he was \"deeply disappointed\" over the Security Council\'s failure on Thursday to agree a strong resolution on Syria. \"I again urge the international community and particularly members of the Security Council, (that) they should be united, for humanity, to deliver a strong message and use whatever available tools under the charter of the United Nations,\" Ban said. As the bloodshed raged, the exodus of Syrians into neighbouring countries intensified. Up to 30,000 Syrians fled into Lebanon in the 48 hours to Friday, the UN refugee agency said.