Government troops heavily shelled rebellious districts in the resistance stronghold of Homs Tuesday, killing at least seven people and compounding fears of a new round of bloody urban combat in a country careening toward all-out civil war.

Activists said the intense shelling of Baba Amr in Homs lasted a few hours but did not seem to be the start of a widely expected military offensive aimed at retaking rebel-held neighbourhoods in the central region. One of the seven people killed in the shelling of Baba Amr was a child, according to the British-based Syrian Observatory for Human Rights, which relies on a network of activists on the ground.

An activist inside the city said the shelling started after repeated attempts by troops to storm the edges of Baba Amr.

"Government troops have been unable to advance because of stiff resistance from defectors inside," he told The Associated Press on condition of anonymity, fearing government reprisals.

The military sent columns of tanks and other reinforcements toward Homs on Monday, activists said. A flood of military reinforcements has been a prelude to previous offensives by President Bashar Assad's authoritarian regime, which has tried to use its overwhelming firepower to crush an opposition that has been bolstered by defecting soldiers and hardened by 11 months of street battles.

On Monday, the Red Cross said it was trying to broker a cease-fire among all parties in Syria to allow emergency aid in.

On Tuesday, Russia said the United Nations should send a special envoy to Syria to help co-ordinate security issues and the delivery of humanitarian assistance. Russia's Foreign Ministry said on Twitter that it's proposing that the U.N. Security Council ask the U.N. Secretary General to send the envoy.

Despite the humanitarian activity, activists reported heavy shelling of the Baba Amr, Khaldiyeh and Karm el-Zeytoun districts -- all in Homs. It lasted for more than two hours early in the morning, followed by intermittent attacks concentrated on Baba Amr.

Baba Amr on Homs' southwest edge has become the centre of the city's opposition. Hundreds of army defectors are thought to be taking shelter there, clashing with troops in hit-and-run attacks each day.

Phone lines have been cut with the city, making it difficult to get firsthand accounts from Homs residents.

Rami Abdul-Rahman, who heads the Observatory, said there was no indication yet that a major ground assault to take back Baba Amr had begun.

Russia's U.N. Ambassador Vitaly Churkin said Monday the world body should help solve humanitarian issues in Syria.

Russia and China have vetoed two Security Council resolutions backing Arab League plans aimed at ending the conflict and condemning Assad's crackdown on protests that killed 5,400 in 2011 alone, according to the U.N. Hundreds more have been killed since, activist groups say. One of the groups puts the toll at more than 7,300.

Russian Foreign Ministry spokesman Alexander Lukashevich also said Tuesday that Moscow will not attend the planned "Friends of Syria" meeting at the end of this week, because its organizers had failed to invite representatives of the Syrian government.

Lukashevich said the meeting in Tunisia wouldn't help a dialogue, saying that the global community should act as friends of the entire Syrian people, and not just one part.

"It looks like an attempt to forge some kind of international coalition like it was with the setting-up of a 'Contact Group' for Libya," Lukashevich said.

Russia has said it will block any U.N. resolution that could pave the way for a replay of what happened in Libya. In that case, Russia abstained from a vote, which cleared the way for months of NATO air force attacks that helped Libyans end Moammar Gadhafi's regime.