At least 42 people have been killed and more than 400 wounded in two huge bomb attacks in Lebanon's northern city of Tripoli.
The blasts, near mosques, are thought to be the deadliest attack in Lebanon since the end of the civil war in 1990.
War in neighbouring Syria has raised sectarian tensions between the city's Sunni Muslim and Alawite communities.
The blasts came a week after a car bomb in a Shia district of the capital Beirut killed 27 people.
Prominent Sunni Muslim cleric Sheikh Salem Rafii could have been the intended target of the latest attacks, BBC Arabic reports from Beirut. He was unharmed.
The cleric is opposed to Lebanon's militant Shia Hezbollah group and has previously urged young Lebanese men to join opposition fighters in Syria.
UN Secretary-General Ban Ki-moon has condemned the attacks and called for calm and restraint. Meanwhile the UN Security Council called for "people to preserve national unity".
The first bomb hit the al-Taqwa mosque shortly after Friday prayers ended. Minutes later, the second blast struck the al-Salam mosque in the Mina area.
It is not clear if Sheikh Salem Rafii was at the al-Taqwa mosque, although some reports say he was giving a sermon.
In a TV interview after the blast he called for restraint. "We do not want to destroy the country. We want to safeguard the country and preserve Tripoli and its people," he said.
"We should not rush towards reacting. God willing, there is enough time to hold consultations, investigate the matter and know the results."
'Like an earthquake'
Ambulances rushed to the scene of the blasts and a pall of black smoke covered the area.
"It was as if there was an earthquake, the whole city seemed to be shaking," a local resident told Lebanon's Daily Star newspaper.
Television pictures showed cars on fire and people trying to carry the wounded to safety.
Bodies could be seen on the ground and windows were broken on surrounding apartment blocks.
The preacher at the al-Salam mosque - the site of the second explosion - is also an opponent of the Syrian government and its Lebanese ally, Hezbollah, Associated Press reports.
No group has said it carried out the latest attacks.
In a statement reported by Lebanon's National News Agency, Hezbollah strongly condemned the blasts.
The group said the attacks aimed to "sow seeds of strife among the Lebanese and drag them into bickering under a sectarian guise".
Outgoing Lebanese Prime Minister Najib Mikati and President Michel Suleiman also condemned the attacks, calling on citizens to unite against violence.
A spokesman for UN Secretary-General Ban Ki-moon said: "The secretary-general calls on all Lebanese to exercise restraint, to remain united, and to support their state institutions... in maintaining calm and order in Tripoli and throughout the country, and in preventing the recurrence of such destructive actions."
In a statement, the UN Security Council "appealed to all Lebanese people to preserve national unity in the face of attempts to undermine the country's stability".
The council "stressed the importance for all Lebanese parties to... refrain from any involvement in the Syrian crisis".
Tripoli, a city of nearly 200,000 people and Lebanon's second largest, is one of the country's most volatile sectarian fault lines, with a small Alawite population living in the midst of a Sunni majority.
The Alawite community tends to support Syrian President Bashar al-Assad, with Sunnis mostly backing the rebels fighting him.
The bombs come a week after a massive car bomb rocked a Shia district of Beirut, leaving 27 people dead. The area hit contained Hezbollah strongholds.