(Reuters) – Syrian army armored vehicles have clashed with rebels in Damascus in what residents said was the heaviest fighting in the capital since the revolt against President Bashar al-Assad began 17 months ago.

The spread of hostilities into the Syrian capital comes as United Nations envoy Kofi Annan is visiting Moscow to promote a peace plan for Syria. On Tuesday, he will meet President Vladimir Putin, who has resisted Western calls to increase pressure on Assad.

Talks between Putin and Annan are not expected to break any new ground after Russian Foreign Minister Sergei Lavrov said Western attempts to threaten Syria with further sanctions amounted to blackmail.

Armored vehicles rolled into the southern Damascus district of Midan on Monday and were reinforced by security forces surrounding the area. Residents said they saw snipers deployed on rooftops.

“There are troops everywhere, I can hear ambulances,” said a resident near Midan. “It feels like a war in Damascus.”

A video uploaded by opposition activists aired on al-Jazeera television showed men in jeans hiding in sandbagged alleyways, firing rocket-propelled grenades and machine guns. It was the second straight day of fighting in Midan and Tadamon after major battles on Sunday.