Intense fighting rocks Syrian capital BEIRUT - Syrian government forces backed by armored vehicles and helicopter gunships fought pitched battles with rebels Tuesday in Damascus as the 16-month-old Syrian uprising crept closer to the core of President Bashar al-Assad's rule. Opposition activists reported fighting in at least four neighborhoods across the capital for a third day, and the state-run Syrian Arab News Agency (SANA) said troops on Tuesday were chasing "terrorist elements" in the city. The Britain-based Syrian Observatory for Human Rights said explosions and gunfire were heard in the Midan neighborhood of Damascus and that rebel fighters attacked a police station in Sabeena on the outskirts of the capital. Rebels said government forces were firing mortars in the city and suburbs. The fighting came as top U.N. officials pursued efforts to get Russia and China to support a tougher international response to the Assad government. The U.N. special envoy for Syria, Kofi Annan, was scheduled to meet with Russian President Vladi­mir Putin in Moscow, where the government is coming under strong diplomatic pressure to sign on to a U.N. resolution that would impose strict sanctions on the Assad regime. U.N. Secretary General Ban Ki-moon was traveling to China for talks on Wednesday with President Hu Jintao ahead of a U.N. Security Council vote this week on a Western resolution. In addition to sanctions, the proposed measure invokes Chapter 7 of the U.N. Charter, which authorizes actions that could eventually include military force. The escalation in fighting in Damascus, along with the possibility of increased economic pressure, could turn out to be the most serious challenge yet for Assad's beleaguered 12-year rule. Deepening his isolation, Morocco on Monday ordered the Syrian ambassador to leave the North African kingdom and called for a transition to democracy in Syria. The Assad government retaliated by ordering the expulsion of Morocco's ambassador to Syria. But Russia has remained steadfast in its refusal to abandon its alliance with the government in Damascus. A Russian ship carrying repaired helicopters - which had set sail for Syria under a Curacao flag but turned back when it lost its insurance - is expected to sail to Syria from St. Petersburg, according to the Interfax news agency. Russia says it is not arming Assad but is complying with existing maintenance contracts. At the United Nations, American and European diplomats on Monday abandoned an effort to adopt a Security Council statement condemning Syria's "outrageous use of force" last week in the western village of Tremseh, citing Russia's decision late Friday to block the statement. The Security Council remained deeply divided, with the United States and its European allies favoring the adoption of a resolution threatening sanctions against Damascus if it failed to halt its shelling of residential areas. Russia's vehement opposition to sanctions has raised concerns that it may be preparing its third veto of a Western-backed resolution aimed at punishing Assad for his excessive use of force in civilian areas.