Troops and police are on alert in the northern Nigerian city of Kaduna, amid fears that further conflict could follow Friday's Muslim prayers.

Hundreds of people were killed Kaduna ealier this week, as Muslims and Christians clashed over the proposed introduction of Islamic Sharia law in the state.

The security forces are guarding mosques to head off possible violence.

As work begins to clear up Kaduna, government officials say they now believe about 220 people were killed in this week's clashes.

But hospital officials have spoken of 300 bodies being brought in, and eyewitnesses have seen scores of bodies lying in the streets.

Homeless

Military reinforcements have restored an uneasy calm to the city, but hundreds remain homeless after houses were set alight.

Papal plea

Pope John Paul has meanwhile urged Nigerians to respect religious freedom.

"I have learned with deep pain that in Nigeria tensions have caused many deaths," the Pope said during the second day of his visit to Cairo.

Several states in Nigeria's Muslim-dominated north have taken steps towards implementing Sharia law - a spin-off from the greater political freedoms following Nigeria's return to democracy last year.

Zamfara, with an overwhelmingly Muslim population, was the first state to implement Sharia, and the transition passed off peacefully.

But in Kaduna, a larger state with a substantial Christian majority, the proposed introduction of the Islamic legal code proved particularly divisive.

Nigeria's Human Rights Law Service has meanwhile begun court proceedings to try to have Sharia declared unconstitutional in Zamfara.

But other predominantly-Muslim states in northern Nigeria have taken steps to introduce Sharia law.

The governors of Niger and Sokoto states have both signed bills under which Sharia is expected to come into effect in May.

Two others states - Kano and Yobe - are considering similar moves.

Muslims are pressing for its wider introduction, and have repeatedly stressed that Sharia will not affect Christians.