Fighting in Baghdad's Shi'ite slum of Sadr City made April the deadliest month for Iraqi civilians since last August and for U.S. troops since last September, figures obtained on Wednesday showed.

Iraqi Health Ministry figures showed 968 civilian deaths in April, the most in eight months. On Wednesday the U.S. military reported the deaths of five more of its soldiers in Baghdad, raising its monthly toll to 49.

Most of the U.S. and Iraqi deaths were in the capital, where U.S. and government forces have been fighting Shi'ite militants loyal to anti-American cleric Moqtada al-Sadr in the tightly-packed Sadr City slum and other Shi'ite areas.

U.S. forces said they killed another 16 fighters in gunfights, tank battles and strikes from drone aircraft, following heavy fighting on Tuesday in which they killed 34.

Prime Minister Nuri al-Maliki, who launched a crackdown against Sadr's Mehdi Army militia a month ago in the southern city of Basra, said on Wednesday the government would disarm the fighters by force if they refuse to lay down their weapons.

Two hospitals in Sadr City said they alone had received the bodies of 421 Iraqis killed and treated more than 2,400 wounded since late March. Many of the dead and wounded have been civilians, caught in the crossfire in the crowded slum.

Some of the heaviest fighting has taken place in the past three days, with militiamen taking advantage of blinding dust storms that ground U.S. attack helicopters to launch large-scale ambushes of U.S. and Iraqi positions.

U.S. forces have responded with tank fire and surface-to-surface missiles, destroying buildings.

Thirty-four bodies and 112 wounded victims were brought to the two Sadr City hospitals in the last 24 hours, hospital officials said.

U.S. forces reported three soldiers killed in Baghdad overnight and another two killed on Wednesday afternoon.

April's U.S. death toll is the highest since September 2007, when 65 U.S. soldiers died in Iraq, according to official figures tracked by icasualties.org, an independent website.

The tolls for both soldiers and civilians are still far lower than a year ago, however. In April 2007, 104 U.S. service members and 1,506 Iraqi civilians were killed.

U.S. commanders say the sectarian violence between Sunni Arabs and Shi'ites that characterised earlier years remains sharply lower. But the uprising by Shi'ite militia over the past month has reversed a long trend of declining violence.

MALIKI SETS CONDITIONS

Maliki aimed some of his toughest language yet at the Shi'ite fighters on Wednesday, singling out the Mehdi Army by name and grouping it with Sunni Arab groups like al Qaeda as organisations that must be dissolved.

He set down four conditions - that militias disarm, stop interfering in state affairs, stop running their own courts and hand over wanted fugitives - or face a military assault.

"To refuse these conditions means the continuation of the government's efforts to disarm them by force," Maliki said at a news conference inside Baghdad's fortified Green Zone government and diplomatic compound.

"There is no alternative to these conditions. The alternative is the continuation of force and clashes until we reach the end, to get rid of the weapons and the gangs who are carrying weapons."

Maliki, himself a Shi'ite, launched a crackdown against Mehdi Army fighters last month in the southern city of Basra.

After initial setbacks, the Basra offensive appears to have been a success in driving fighters from the streets there. But the militiamen remain in control of much of Baghdad's Sadr City.