At least eight people were killed and dozens injured when two bombs exploded near an Islamic seminary in the southern Pakistani city of Karachi, witnesses and police officials said.
Both devices went off near a restaurant next to the Sunni religious school in the restive port city, which has been riven for decades by sectarian violence.
"There was an explosion in a restaurant close to Jamia Binoria seminary which was followed by another big blast caused by a bomb fitted in a motorbike parked outside the restaurant," said city police chief Fayyaz Leghari.
An AFP reporter said bodies of four seminary students were seen in the city's Abbasi Shaheed Hospital.
The four, including a six-year-old child died at the hospital, doctors said.
Police have defused a third explosive device found near the blast site, senior officer Tariq Jamil told AFP.
"The explosive device was found in a bag but the bomb disposal squad had defused it," he said.
The defused device weighed at least two kilograms (4.4 pounds).
Police have tightened security around Shiite and Sunni centres, Jamil said.
"We have deployed police and paramilitary forces in the city as preventive measures," he said.
Jamia Binoria has some 3,000 students including foreigners. It was for the first time that it has been targetted.
Hayan Ahmed, an 18-year-old religious student, said he was eating snacks and drinking tea at the restaurant when the first bomb went off and as he came out he was injured by the second blast.
Mohammad Yar, a teacher at the Islamic seminary, or Madrassa, told reporters outside the hospital: "The Madrassa was the target and at this stage we don't want to blame anyone."
Yar said it was the government had to arrest the culprits.
"Every second day there have been blasts in Shiite and Sunni mosques, Islamic seminaries and other places, so whom we should blame?" he said.
Karachi has seen decades of by bloodletting between Sunni and Shiite Islamic sects, ethnic groups and political organisations.
Some 4,000 people have been killed in political, ethnic and sectarian violence in Karachi in the past five years.
The city, Pakistan's industrial and commercial center, witnessed two deadly suicide attacks on Shiite mosques in May that killed 48 people and injured about 150.
A bomb explosion killed two people and injured four others in Karachi on Saturday. The bomb went off outside a car showroom in the city's southern residential district.