Twenty-one people were killed and about 100 others injured in a mortar attack on a Baghdad-area prison, stopping short a cautious optimism over a truce deal in the nearby flashpoint town of Fallujah.

The United States launched a diplomatic offensive Tuesday to keep its coalition in Iraq from splintering after Honduras followed Spain's lead in announcing their troops' withdrawal.

Eighteen mortar rounds rained down late in the afternoon on the coalition-run Baghdad Confinement Facility at Abu Gharib, west of the Iraqi capital, said Brigadier General Mark Kimmitt, the U.S.-led coalition's deputy director of military operations.

Kimmitt said he did not know whether the victims were suspected criminals or "security detainees".

Only kilometers (miles) away, in the Sunni Muslim bastion Fallujah, a first group of 50 families was allowed to return home after two weeks of fighting between US marines and insurgents left hundreds dead and the city in tatters.

"Fifty families were allowed to enter today, 50 families will be allowed tomorrow and 50 the day after that," Lieutenant Colonel Ronny Gordy, of the US marines, told AFP at a roadblock at the eastern edge of the city.

All groups in Fallujah including the insurgents had accepted a truce deal sealed Monday, said a spokesman for the Sunni Muslim Scholars' Association, Muthanna Harith al-Dhari.

A mediator between the two sides, Faud Rawi of the Sunni Iraqi Islamic Party, also said he was "optimistic about the willingness of the fighters to respect the ceasefire".

The deal allows for joint patrols between coalition and local security forces, an amnesty for turning in heavy weapons and the return of families who had fled town.

Local police will also investigate the brutal murder in Fallujah on March 31 of four American contractors, which triggered the US offensive. Previously the coalition had demanded the handover of the killers ahead of any deal.

Rawi said the head of the Iraqi police and the commander of the paramilitary Iraqi Civil Defense Corps had returned to Fallujah and joint patrols with the US marines had begun.

During the April siege of Fallujah, the bloodiest fighting since the U.S.-led invasion of Iraq, more than 600 Iraqis died, according to hospital sources, as well as scores of US troops.

In Washington, U.S. Secretary of State Colin Powell was engaged in marathon telephone diplomacy, saying he would speak with dozens of foreign leaders to gauge their commitment to the U.S.-led coalition in Iraq.

"I am getting solid support for our efforts, commitments to remain and finish the job that they came to do," Powell told reporters, describing his conversations.

Honduran President Ricardo Maduro announced late Monday that his country's 368 soldiers in Iraq would be withdrawn as soon as possible, saying they had accomplished the mission assigned them by the United Nations.

The announcement came hot on the heels of Spain's decision to pull out its 1,432 troops from Iraq immediately.

The Hondurans, who serve as part of the Spanish-led Plus Ultra unit in the swathe of south-central Iraq under Polish command, were ordered by Defense Minister Federico Breve to halt their patrols of Najaf, the holy city where firebrand militia leader Moqtada Sadr is holed up.

Aside from Spain and Honduras, 32 countries have deployed more than 155,000 forces in Iraq under the U.S.-led "coalition of the willing".

Of the two withdrawing powers, Powell said: "We thank them for what they have done (and) regret that they find it necessary to leave at this point".

Madrid's move however drew a strong reproach from U.S. President George W. Bush Monday.

In a conversation with Spanish Prime Minister Jose Luis Rodriguez Zapatero, Bush "stressed the importance of carefully considering future actions to avoid giving false comfort to terrorists or enemies of freedom in Iraq", said spokesman Scott McClellan.

After the defection of the sixth-largest troop contingent in Iraq, other coalition members -- including Britain, Australia, Japan, Italy and Poland -- have hastened to confirm they will remain engaged.

South Korea, too, which has 400 people on the ground in Iraq but has pledged to deploy up to 3,600 more, sent reassurance it would not be swayed by Madrid's pullout. Its contingent is to head to northern, Kurdish-run Iraq and only conduct relief and rehabilitation work.

The White House insisted the coalition was not fraying.

"The coalition in Iraq is strong," McClellan said Tuesday in Buffalo, New York.

But Thailand warned that its 400 soldiers, stationed in Karbala under Polish command, would be pulled out if Iraq became so dangerous that they were unable to carry out their mission.

"The safety of Thai troops in Iraq is my first priority, followed by their humanitarian mission," Prime Minister Thaksin Shinawatra told reporters. "We went there to help them (Iraqis), but if we get killed why do we have to stay?"

Meanwhile, a Republican senator said spiralling violence in Iraq could force the United States to reintroduce the military draft.

"There's not an American... that doesn't understand what we are engaged in today and what the prospects are for the future," Senator Chuck Hagel told a Senate Foreign Relations Committee hearing on post-occupation Iraq.

"If that's the case, why shouldn't we ask all of our citizens to bear some responsibility and pay some price?" Hagel said.(China Daily/Agencies)

Source: Xinhua