At least 17 people have been killed by a car bomb on the outskirts of Syria's capital Damascus, officials have said.
The blast happened near buildings used by security forces at an intersection leading to an important Shia shrine.
Such attacks are rare in Syria, but the country has seen two major assassinations in the past year.
No group has claimed responsibility for the blast, although the Syrian interior minister, Gen Bassam Abdul-Majid, called it a cowardly "terrorist act".
"At the moment, we cannot point to a particular party. However, the ongoing investigations will lead us to the perpetrators," he told Syrian state TV.
The official Sana news agency said a booby-trapped car packed with about 200kg (440 lbs) of explosives had blown up at 0845 (0545 GMT) on the road to the international airport to the south of the capital, in an area crowded with civilians.
People in Damascus have been shocked by the rare attack
Security forces cordoned off the scene of the blast, which was some 8km (5 miles) from the al-Sayyida Zeinab shrine, one of Syria's holiest sites and a popular place of pilgrimage for Iraqi, Iranian and Lebanese Muslims.
All the dead are reported to be civilians. At least 14 others were wounded.
The security complex, which reportedly houses a directorate of the intelligence services that deals with Palestinian militants and political activists, suffered little damage.
The blast was the deadliest single attack in Damascus since 13 March 1986, when a bombing blamed on Iraqi agents left 60 people dead.
A month later, 144 were killed by series of bombings in five towns across Syria. The perpetrators were believed to be pro-Iraqi militants.
Footage broadcast on Syrian TV showed a large crater filled with water at the site of the explosion. The remains of a destroyed car were strewn across the main road, witness said.
Nearby vehicles and buildings, including a school that was empty because of the weekend, were left with shattered windows.
We felt a very strong explosion - we thought it was an earthquake
One witness told Syrian TV that he had thought the blast was an earthquake.
"We felt a very strong explosion," said the man, who did not give his name.
"We walked outside... the whole building collapsed. Five members of my family were wounded and are in hospital."
Syria's Minister of Religious Endowments, Muhammad Abdul-Sattar al-Sayyid, said it was shocking that such an attack had occurred in the run-up to the feast-day of Eid al-Fitr, which marks the end of the Islamic month of Ramadan.
He said that such acts were counter to the spirit of all religions and were only condoned by what he described as "the enemies of justice", chief among which he said was Israel.
US state department spokesman Gordon Duguid said it "condemned the bombing and all terrorist actions", and that the US embassy in Damascus would close its consular section until Tuesday because of security concerns.
Car bomb attacks are rare in Syria and the attack will be disturbing for the Syrian government, which prides itself on stability, says the BBC's Natalia Antelava in Beirut.
Its critics say that stability comes at the price of democracy, says our correspondent.
This is believed to be the first car bombing since a senior Hezbollah military commander, Imad Mughniyeh, was assassinated in Damascus in February.
The leader of the Lebanese Shia Islamist movement, Sheikh Hassan Nasrallah, subsequently blamed Israel for the blast, although Israel denied any involvement.
In August, a senior military official close to President Bashar al-Assad was shot dead, in as-yet unexplained circumstances, at a beach resort near the port city of Tartus.
Brig Gen Mohammed Suleiman had responsibility for sensitive security issues and was described as Syria's "main interlocutor" in a UN inquiry into the country's alleged nuclear activities.
On Friday, the director of the International Atomic Energy Agency, Mohamed ElBaradei, said Mr Suleiman's death would delay the inquiry.
BBC Middle East analyst Andrew Bolton says that although there will be a great deal of speculation about who was behind this latest attack, one area the authorities are reported to be looking at is the possibility that it was the work of Islamist militants.
The blast shattered windows of nearby vehicles and buildings
There were similar attacks before the authorities moved strongly against by Islamist groups, particularly the Muslim Brotherhood, during the 1980s.
In recent years, there have been some reported clashes, with the security forces killing several suspected Islamist militants, and arresting hundreds more. There has also been recent unrest involving Islamist prisoners in Syrian jails.
Our correspondent says Saturday's attack has come at a time when Syria is at a political crossroads.
Earlier this month, Syria took part in talks with Turkey, Qatar and France, which currently holds the EU presidency, in a bid to boost efforts towards peace in the Middle East.
Mr Assad said he hoped the summit would form a basis for direct peace talks with Israel, with which Syria has been at war since its neighbour's foundation in 1948.
But despite the new-found willingness to talk, there are still tensions between the Syrians and Israelis, our correspondent says.
Divisive issues include Syrian support for groups like the Palestinian Islamist movements, Hamas and Islamic Jihad, and Hezbollah.
Syria has also faced diplomatic isolation since the assassination of former Lebanese Prime Minister Rafik Hariri in 2005. Syria's critics have blamed it for the murder but it denies any involvement.
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