Although only three people were injured, the bombing had greater symbolic importance as a sign of the ability of rebels - assuming they were responsible - to hit the heart of the Assad regime. State television showed a black plume of smoke and reporters on the scene described the mangled wreckage of cars.
As well as the internal threat, the Syrian president is now facing significant pressure from Turkey, once an ally but which is now one of his severest critics.
Yesterday, Turkey sent missile batteries, tanks and troops to the border as a "security corridor" after Syria shot down a Turkish warplane which briefly intruded into its air-space last Friday. About 30 military vehicles had accompanied by a truck towing missile batteries from a base in the southeastern province of Hatay.
Turkey's change of heart on Mr Assad has been dramatic. The two countries nearly came to war in the 1980s and 1990s, but that was when Turkey, a staunch Nato ally, was developing close ties including a military and strategic alliance with Israel.
When the moderate Islamist party of the prime minister, Recep Tayyip Erdogan, came to power, he sought to rebalance relations with neighbours including Syria and Iran. That all changed with the violence of Mr Assad's reaction to protests against his rule.
Along the border on Thursday, there was a high police presence and civilian vehicles were being kept away. The many Syrian activists and rebels who have sought sanctuary on the Turkish side were excited at the possibility that the outside intervention on the opposition's behalf they had long sought might soon be on its way.
"We have been asking the Turkish to do this for a long long time," said Dr Munzer Yazji, who heads a team of medical staff in the town of Hatay working to supply networks of secret field hospitals inside Syria, some in the border areas.
"Our hospitals are being targeted by shelling, or doctors are being killed. Before the Syrian soldiers could come within metres of the border. Now we wish very much that this will provide some protection."
Fighters with the rebel Free Syrian Army said they believed the Turkish troops were making the first preparations for the establishment of a buffer region in northern Syria, of which an air exclusion zone would most likely be part.
"We are told that any Syrian army that comes within 5km of the Turkish border will be hit," said Ahmed, a coordinator, claiming to have inside information.
Large areas inside northern Syria are now in opposition hands. Mr Assad's troops still have the benefit of overwhelming firepower, but the opposition has begun receiving supplies of light arms from backers in Qatar and Saudi Arabia, and is able to regain territory lost in heavy assaults.
Although it has nothing like the territorial control exercised by the rebels in eastern Libya in the civil war there last year, they felt secure enough to give a guided tour earlier this week to Burhan Ghalioun, until recently the leader of the opposition Syrian National Council.
They are also increasingly able to repel assaults. According to activists, a full-scale tank assault on the major city of Deir Al-Zour, near the border with Iraq, was brought to a halt yesterday by a rebel counter-attack. It had been preceded by a week of shelling and helicopter attacks, in which scores of people died.
There was also heavy fighting in the town of Douma, on the northern outskirts of Damascus.
On Wednesday, rebels attacked the headquarters of a pro-regime satellite television station, killing seven people, while the day before, there was a major gun-battle on the city's previously quiet western outskirts.
The Syrian Observatory for Human Rights, a London-based activist group which collates casualty figures, said that 4,700 people had been killed in the country since April 12, when a UN-sponsored ceasefire was called.