Syria moved armored vehicles into the capital Damascus as opposition fighters battled Syrian government forces in what residents described as the fiercest fighting yet inside the capital.

Activists said Monday the fighting had spread to several neighborhoods and in the center of the city.

The spread of fighting came as U.N. peace mediator Kofi Annan was due to fly to Moscow to meet Russian President Vladimir Putin who has resisted Western calls to increase pressure on Syrian leader Bashar al-Assad.

Russian Foreign Minister Sergei Lavrov, on Monday, accused the West of using 'blackmail” to pressure Moscow into backing a stronger U.N. resolution against Syria.

On Sunday, the International Committee of the Red Cross said there is a state of civil war across more parts of Syria, widening its earlier designation.