Gunmen in Syria have staged an ambush that killed a senior state prosecutor and a judge in an attack that suggests armed factions are growing bolder and more co-ordinated in their uprising against President Bashar Assad's regime.

The roadway killings on Sunday in an opposition-dominated northern region came a day after a deadly hit-and-run attack on a political figure in the heart of the pro-Assad city of Aleppo.

The assassinations have not reached Assad's inner circle but they indicate a shift toward violent tactics by the opposition as it recruits more military defectors and seeks to tighten control over the small pieces of territory in its hands.

The targeted killings happened on a road in the north-west province of Idlib, which has become a patchwork of areas held either by the government or mutinous soldiers who have safe havens in neighbouring Turkey.

The state news agency Sana said gunmen opened fire on a car carrying the Idlib provincial state prosecutor, Nidal Ghazal, and Judge Mohammed Ziadeh. Both were killed instantly and their driver died of injuries later.

Idlib has witnessed intense clashes between troops loyal to Assad and army defectors who attack and then hide in the rugged mountains. In June the town of Jisr al-Shugour became the first area to fall into the hands of rebels, who were accused by the government of killing scores of people and setting government buildings on fire. Syrian troops loyal to Assad retook the area shortly afterwards.

On Saturday, Sana said gunmen shot dead Jamal al-Bish, a member of the city council of the nearby northern city of Aleppo. The city has been a centre of support for Assad since the uprising began.

On 11 February, Brigadier General Issa al-Khouli, a doctor and the chief of a military hospital in the capital, was shot and killed as he left his home in Damascus. Last month, the head of the Syrian Arab Red Crescent branch in Idlib was shot dead on his way to Damascus.

Fears of civil war in Syria have led to neighbouring Jordan racing to finish a refugee camp near the border to handle the possible exodus of people fleeing for safety.

Egypt is the latest Arab nation to publicly snub Assad by ordering the withdrawal of its ambassador from Damascus.

The Syrian government has offered some concessions, including proposing a referendum next week that could allow more political voices to challenge Assad's Ba'ath party. But the opposition will accept nothing short of Assad's resignation. The regime has not eased off its attacks on opposition forces, which it describes as "terrorists" carrying out a foreign conspiracy to destabilise the country.

In Homs, central Syria, government forces sent in reinforcements as they shelled the rebel-held Baba Amr district that has been under near constant barrage for nearly two weeks, said the UK-based Syrian Observatory for Human Rights. The group said at least 14 people were killed on Sunday across Syria, half of them by government troops.

"I'm worried that Syria is going to slide into a civil war," William Hague, the UK foreign secretary, told the BBC on Sunday.

The UN last gave a death toll for the conflict in January, claiming 5,400 people had been killed in 2011 alone. But hundreds more have been killed since, according to activist groups. An opposition group, Local Co-ordination Committees, says more than 7,300 have been killed since the uprising began 11 months ago.

There is no way to independently verify the numbers, since Syria bans almost all foreign journalists and human rights organisations.

In Cairo, the Egyptian state news agency, Mena, said the foreign minister, Mohammed Amr, had decided to withdraw the country's ambassador to Syria. The report gave no reason for the decision, but Arab governments have been pulling back diplomatic backing for Assad in protest at his refusal to back regional peace efforts.

Earlier this month, the six-nation Gulf Co-operation Council, led by Saudi Arabia, said it would withdraw its ambassadors and expel Syrian envoys from the oil-rich region. Tunisia has pulled its ambassador from Damascus.