Syrian activists say clashes between rebels and government forces in the capital, Damascus, have continued for a third day, in what has been the heaviest period of fighting in the city since the revolt against President Bashar al-Assad began.

The fighting Tuesday, which activists said included the use of helicopter gunships, comes as the U.N. Security Council debates two competing resolutions on Syria.

Britain, France, Germany and the United States are pushing for a 45-day renewal of the U.N. observer mission in Syria along with a threat of sanctions against the Assad government. Russia's proposal calls for a longer extension of the mission, but no sanctions.

U.N. Secretary-General Ban Ki-moon is visiting China, while U.N. envoy Kofi Annan holds talks with Russian President Vladimir Putin in Moscow.

Both Russia and China have vetoed previous Western-backed Security Council resolutions calling for tough action against Syria.