DAMASCUS - Syrian rebels shelled a key area of Damascus home to President Bashar al-Assad's Alawite minority, embassies and government buildings on Wednesday, as they stepped up attacks on the capital.

Britain, meanwhile, said it was to open talks with the rebels in a bid to help end the violence, as the main opposition Syrian National Council said it hoped resolving the conflict would top re-elected US President Barack Obama's agenda.

The shelling of the mainly Alawite Mazzeh 86 district came a day after a car bomb hit another Alawite area in the suburb of Qudsaya, as rebels increasingly target Assad's supporters in the minority, an offshoot of Shiite Islam.

Sectarian divides are a key factor in the Syrian uprising, with many in the country's Sunni Muslim majority frustrated at more than 40 years of Alawite-dominated rule.

State news agency SANA reported that the shelling had hit a home and mini-bus carrying passengers in Mazzeh 86, which lies beneath Assad's hilltop presidential palace, killing at least three civilians.

The Syrian Observatory for Human Rights, a Britain-based watchdog that relies on a network of activists and medics on the ground, confirmed the shelling and said three civilians were killed and 12 wounded.

It has previously reported a car bombing in Qudsaya on Tuesday that killed 19 people and another on Monday in Mazzeh, likewise in the capital, that left 13 dead.

Rebel fighters were also clashing with pro-regime Palestinian forces in the southern Hajar al-Aswad district and the nearby Palestinian refugee camp of Yarmuk, the Observatory said, as the area becomes another focal point of violence.

Home to some 148,000 residents, the camp has been the scene of fierce fighting between rebels and the Popular Front for the Liberation of Palestine-General Command (PFLP-GC), an ally of Assad.

Pro-regime newspaper Al-Watan said government forces had launched an offensive on the area of Tadamun near the camp to "liberate civilians and hostages" held by the rebel Free Syrian Army (FSA) and protect the Palestinians.

A car bomb also exploded overnight in the southern Qadam neighbourhood, causing at least one death, after violence on Tuesday left a total of 150 dead, including 79 civilians, the Observatory said.

British Prime Minister David Cameron's office said the government had authorised officials to have contacts with military representatives of the opposition, although government sources stressed the initiative was about political dialogue, not providing weapons.

Media reports said Britain's envoy to the Syrian opposition, John Wilkes, would arrange meetings in third countries to initiate talks with the rebels.

British officials said they would make clear to the Syrian groups that they must respect human rights, after a video last week purported to show rebel forces beating and executing pro-regime fighters.

Cameron himself toured a desert refugee camp for Syrians in northern Jordan on Wednesday. "I am hearing appalling stories about what has happened inside Syria so one of the first things I want to talk to Barack about is how we must do more to try and solve this crisis," he said.

As the opposition Syrian National Council met in the Qatari capital Doha for talks, leading SNC member Radwan Ziadeh said Obama should work to end the crisis following his re-election.

"We hope President Obama places Syria among the priorities in his foreign policy to put an end to the crisis and achieve the aspirations of the Syrian people to choose their own government and their own president, just like the American people did," Ziadeh said.

The US has voiced increasing frustration with the SNC for not fully representing the opposition and the talks in Qatar will see an initiative put forward to form a new government-in-exile to represent the opposition.

Rights groups say more than 36,000 people have died since the uprising against Assad's regime erupted in March 2011, first as a protest movement inspired by the Arab Spring and then an armed rebellion.