An explosion rocked a Coptic church near Libya's third-largest city of Misrata killing two Egyptians and wounding two others, the Egyptian embassy and state media reported Sunday, as Cairo condemned the blast.
Libya's official LANA news agency said the attack took place late Saturday after mass as people were leaving the church. There was no immediate claim for the blast.
"Unknown assailants targeted a church building in the town of Dafniya, in Misrata (province), causing the death of two Egyptian citizens and wounding two others," LANA reported.
"The explosion happened after the mass ended and people were on their way out," said the agency.
An Egyptian diplomat in Tripoli said the explosion struck the church of Mar Girgis (St George) at around 11:30 pm (2230 GMT) on Saturday but that the embassy was not informed until the morning.
He confirmed that two Egyptians were killed and two others wounded in the attack.
"We still don't have clear information" about what caused the explosion, the diplomat said. But he added that, according to initial reports, the blast took place in an annex of the church.
Atiya al-Dreni, vice-chairman of the Misrata local council told AFP that an investigation was underway. "Explosives experts will determine what happened in the next few hours or days," he said.
"The reasons are unknown... if it was intentional the number of casualties would have been higher."
Egyptian Foreign Minister Mohammed Kamel Amr "denounced" the violence, the state-run MENA news agency reported from Cairo.
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"Egypt is requesting an investigation into the circumstances of the operation and for those responsible to be put on trial," the minister said.
The Egyptian foreign ministry also sent urgent messages to the Libyan interior and foreign ministries requesting beefed up security around the church, MENA added.
The agency said "two unknown assailants had thrown a grenade" at a church building.
Dafniya is a Mediterranean town 30 kilometres (20 miles) west of the city of Misrata, where brigades made up of former rebels hold a major checkpoint.
There were an estimated 1.5 million Egyptians living and working in Libya before the 2011 armed revolt that toppled Libyan dictator Moamer Kadhafi. About two-thirds left during the war but many returned in 2012.
Before the revolt Libya had a population of around 6.3 million -- including some 1.5 million African immigrants many of whom fled during the fighting -- that was 97 percent Muslim and only three percent Christian.
Christians in Libya are mostly expatriates, including migrant workers from neighbouring Egypt where Coptic Christians are the largest religious minority.
In August, the International Committee of the Red Cross shut its operations in Misrata, 180 kilometres (110 miles) east of the capital, after armed assailants laid siege to a staff residence.
Libya's first elected authorities are keen to boost security but the fledgling army and police are often helpless in the face of well-armed militias made up of former rebels.
Extremism has become a source of growing concern in post-Kadhafi Libya, with several international agencies and diplomatic missions targeted this year by attacks blamed on radical Islamists.
The deadliest was a September 11 assault on the US consulate in second city Benghazi, which killed ambassador Chris Stevens and three other Americans.