Syrian opposition groups are calling for protests Sunday in the capital Damascus and elsewhere to commemorate the one-year anniversary of the first nationwide demonstrations of the country's uprising.

Many activists consider 18 March 2011 the start of the uprising against authoritarian President Bashar Assad. On that day, thousands took to the streets in cities across Syria, and security forces killed marchers in the southern city of Daraa.

Since then protests have spread and many in the opposition have taken up arms to defend themselves and attack government forces as the conflict has grown more militarised.

The UN says more than 8,000 people have been killed.

It is unclear if demonstrations will go ahead Sunday in Damascus, an Assad stronghold. Tens of thousand rallied there in support of the president last week.

On Saturday, three suicide bombings there killed 27 people. The government blamed them on the opposition, which is says is made up of "terrorist" groups acting out a foreign conspiracy. Some opposition leaders accused the regime of complicity in the attacks to tarnish the uprising. No group has claimed responsibility.

International diplomacy has failed to stop the bloodshed.

The US and many Arab and European countries have called on Assad to step down, but Russia and China have protected Syria from censure by the UN Security Council. They warn against foreign intervention and fear that an anti-regime resolution could open the door to an international military campaign, as happened against Moammar Gaddafi in Libya last year.

Joint UN-Arab League envoy Kofi Annan is sending a team to Damascus Monday for meetings with the regime.

In recent talks with Assad in Syria, Annan pushed for an immediate ceasefire to allow for dialogue among all parties on a political solution.

Syria responded to Annan in a letter seen by The Associated Press on Friday that it is "keen to end violence" but insisted that rebels give up their weapons first.

The Syrian response falls short of US and European demands that regime forces stop fighting first — and even Russia's insistence that both sides stop fighting simultaneously.

Most leaders in Syria's disorganised opposition reject talks with the regime, saying it has killed too many people for dialogue to be an option.