At least two people have died and many are injured after an apparent suicide bomb attack on a housing complex in Saudi Arabia's capital, Riyadh.
A number of buildings were destroyed at the compound
The attack, shortly after midnight (2100 GMT) on Sunday, hit the Muhaya residential compound in the west of the capital and left many children among the wounded.
Saudi officials have said that the attack bore the hallmarks of an al-Qaeda suicide bombing.
"This is a crime against innocents which is in the style of
al-Qaeda, it is an al-Qaeda operation," said a Saudi security source quoted by Reuters news agency.
The explosion came a day after the United States shut its diplomatic missions in Saudi Arabia after "credible evidence" of a threat and the UK embassy in Bahrain issued a similar warning.
The US warned its embassy staff in the Saudi capital to stay at home on Sunday, "pending further assessment of the security situation".
Saudi police in Mecca recently uncovered a suspected al-Qaeda cell believed to be planning attacks.
Thirty-five people were killed in a string of suicide attacks in May on a Western compound in Riyadh.
The Saudi ambassador in London, Prince Turki al-Faisal, condemned the attack as "a terrible event carried out by evil people whose sole aim is the destruction of the kingdom".
The Muhaya compound contains about 200 houses, mainly home to foreigners from the Arab world - including Lebanese, Egyptians and Syrians.
There are no confirmed foreign fatalities, but one American is wounded and another missing, according to a US official.
No US diplomatic staff live in the compound, which is several kilometres away from the diplomatic quarter.
The UK Foreign Office said two Britons were unaccounted for.
The compound is near several private residences belonging to the Saudi royal family, according to a Western diplomat quoted by Reuters news agency.
Government officials said that gunmen
tried to enter the compound, and there was an exchange of fire with security guards.
Eyewitnesses said the attackers tried to get through an outer wall, to drive a car bomb as close as possible before detonating it.
Eyewitnesses said a crater five metres wide and two metres deep was left by the blast, and rescue workers are trying to locate anyone trapped under rubble.
It is unknown how many people carried out the attacks.
At least 10 houses are reported to have been destroyed.
"We heard very strong explosion and we saw the fire," Bassem al-Hourani, who said he was a resident at the targeted compound, told Arabic television station Al-Arabiya.
"I heard screams of the children and women... I saw a lot of people injured and I believe there a lot of people dead," he said.
Many of the injured are children who were at home while their parents were out, following the breaking of the Ramadan fast for the day.
During Ramadan, shopping and public life takes place after sunset and people stay out later in the evenings.
The US embassy in Riyadh said on Friday it had "credible information that terrorists in Saudi Arabia have moved from the planning to operational phase of planned attacks in the kingdom."
The statement said: "The embassy strongly urges all American citizens in the kingdom to be especially vigilant when in any area that is perceived to be American or Western."
State Department spokesman Richard Boucher said fears of an imminent attack in the kingdom meant it was "prudent... to warn Americans and to close our operations for a review."
Missions in Riyadh, Jeddah and Dhahran were closed on Saturday.
Britain, Canada and Australia last month issued similar
alerts, which angered Saudi officials, who say they have
made important strides in fighting terror inside the country.
On Thursday, two suspected members of the al-Qaeda cell in Mecca blew themselves up apparently to avoid arrest, while a third suspect was shot dead by security forces in Riyadh.