Details added (first version published at 16:37)
Two powerful explosions at two mosques in Lebanon's northern port city of Tripoli killed at least 43 people on Friday, Lebanese police said, dpa reported.
More than 500 people were wounded in the blasts, which occurred minutes apart, according to the Lebanese Red Cross.
The head of the Lebanese Red Cross, George Kettaneh, told dpa: "We have dozens of injured in critical condition," indicating that the death toll could rise.
A Red Cross volunteer said efforts continued to collect body parts of people blown up in the bombings.
The first explosion took place in the Sunni-dominated district of al-Zaherya, as worshippers were leaving the Taqwa mosque.
The second bombing targeted the Salam mosque in the district of al-Mina.
Lebanese television stations aired footage of bloodied victims and heavily damaged buildings. Men were seen running through the streets calling for "jihad" (holy war) against "the enemies of Islam."
A Lebanese army source at the scene told dpa the car bomb which detonated near al Taqwa mosque was loaded with 100 kilograms of explosives.
One witness, Hosni Kabbara, said he heard the first explosion and a few minutes later heard another powerful blast, which shook his building. His two daughters were injured.
"My daughters, six and eight, were watching cartoons on television, when the whole window of our living room fell on them," Kabbara said.
By nightfall, bearded gunmen had deployed onto some of Tripoli's streets, establishing control points and checking identities.
Tripoli is home to Muslim Sunni extremist groups, with close links to al-Qaeda.
Members of radical Sunni organisations in the city held an urgent meeting following the blasts, and announced that they would protect their areas themselves.
But Sunni moderate leaders called for restraint, emphasizing that the Lebanese army should be the sole protector of the Lebanese people.
Tripoli has recently seen deadly violence between backers and opponents of the armed uprising against President Bashar al-Assad in neighbouring Syria.
Many Lebanese fear these latest explosions, and last week's deadly attack which hit a stronghold of the Shiite Hezbollah movement in Beirut's southern suburbs, are meant to plunge the country into renewed religious strife.
Caretaker Sunni Prime Minister Nagib Mikati, whose house is located near where one of the blasts occurred, denounced the attacks.
"This is more proof that the situation in Lebanon has reached a dangerous state," he said.
Hezbollah, whose militants are currently fighting alongside President Assad's troops in Syria, also condemned the Tripoli blast - as did the Syrian government itself in Damascus.
At the UN, a spokesman said Secretary General Ban Ki-moon wanted to see the perpetrators brought to justice as soon as possible.
"The secretary general strongly condemns the explosion of car bombs outside two mosques," said Eduardo del Buey.