BEIRUT – Syrian rebels fired grenades at tanks and troops while regime armor shelled Damascus neighborhoods Monday, sending terrified families fleeing the most sustained and widespread fighting in the capital since the start of the uprising 16 months ago.

A ring of fierce clashes nearly encircled the heavily guarded capital as rebels seeking to overthrow President Bashar Assad pushed the civil war that has been building in Syria’s impoverished provinces closer to the seat of power.

While the clashes were focused in a string of neighborhoods in the city’s southwest, for many of its 4 million people the violence brought scarily close to home the strife that has deeply scarred other Syrian cities.

In high-end downtown cafes frequented by the business and government elite tightly bound to the Assad regime, customers watched as black smoke billowed on the horizon and the boom of government shells reverberated in the distance.

“Without a doubt, this is all anyone is talking about today,” a Damascus activist who gave his name as Noor Bitar said via Skype.

“The sounds of war are clear throughout the city. They are bouncing off the buildings.”

Syria’s violence has grown increasingly bloody and chaotic in recent months as the uprising has morphed from a peaceful protest movement seeking political change into an armed insurgency seeking to topple the regime by force.

Anti-regime activists say more than 17,000 people have been killed, and the government says it has lost more than 4,000 security officers.

It does not provide the number of civilians that are dead.

International diplomacy has failed to stop the violence, and world powers remain deeply divided over who is responsible and how to stop it. The U.S. and many Western nations have called on Assad to leave power, while Russia, China and Iran have stood by the regime.

On Monday, Russian Foreign Minister Sergey Lavrov accused the West of using blackmail to secure a U.N. Security Council resolution that could allow the use of force in Syria.

International envoy Kofi Annan, who has made little progress in brokering a political solution in Syria, met Russian leaders in Moscow on Monday.

From Britain, the Syrian Observatory for Human Rights said 12 people were killed in and around Damascus, among some 90 people killed nationwide.

About a third of the dead were government troops, it said.