The 30th Infantry Brigade, from North Carolina, and the 39th Infantry Brigade, from Arkansas, each with 5000 soldiers, were ordered to join the active duty force on 1 and 12 October respectively.
They will undergo about three months of training before going to Iraq early next year. The soldiers will serve 12-month tours-of-duty.
The Army also put the 5000-member 81st National Guard Brigade from Washington state on notice for duty in Iraq.
The part-time soldiers from North Carolina and Arkansas had been alerted earlier about the likelihood of service in Iraq, where the United States already has 130,000 troops.
Dearth of foreign aid
"Since it doesn't look like we'll have them [foreign troops], we have no choice but to plan for American forces," John Abizaid, head of the US Central Command, said in an interview with reporters after appearing before the Senate Armed Services Committee earlier this week.
There are currently two multinational divisions in Iraq, each led by Britain and Poland, and the US has been calling for other countries to help form a third multinational division.
"Since it doesn't look like we'll have them [foreign troops], we have no choice but to plan for American forces"
Head of the US Central Command
In a further sign that resistance activities in Iraq against US-led occupation forces are continuing largely unabated, a landmark hotel housing American officials came under mortar or rocket fire on Saturday.
The attack caused minor damage near the top of the Rashid Hotel and no casualties were reported. It came amid a rash of bloodshed that has rattled UN workers and foreign journalists, and resulted in a mounting toll among Iraqi civilians.
US military officials said three or four mortars or rockets were fired at about 23:40 (02:40 GMT) at the 14-story Rashid Hotel, an important symbol of the occupation.
“It woke us up at the back but there was no further impact other than that,” Charles Heatley, spokesman for the occupation authority, told AFP.
The hotel, which is located in central Baghdad, houses senior military and civilian occupation officials.
Separately, the US said on Friday that it is holding 19 al-Qaida suspects among 248 foreign fighters captured in Iraq.
Paul Bremer said 19 al-Qaida members were in US custody in Iraq, Reuters reported. He told reporters in Washington he did not know the nationalities of the al-Qaida suspects.
“It woke us up at the back but there was no further impact other than that”
Spokesman for the occupation authority
But he said a total of 248 foreigners were being held, among them 123 Syrians and a large number of both Iranians and Yemenis.
“That's been a matter that has come out in their interrogations or in their documents,” he responded when pressed on how he knew the 19 prisoners in question were members of al-Qaida, the group accused of the September 2001 attacks on the US.
Washington has said foreign fighters moving into Iraq to oppose US-led occupation forces have become a major "terrorist" problem. But the US has not provided any evidence that al-Qaida is present in Iraq.
The United States has accused Syria of allowing foreign fighters to infiltrate neighbouring Iraq, a charge that Damascus has repeatedly denied.
Bremer said Syrians represented the largest non-Iraqi contingent among the captives.
"I think ... the next two countries are Iran and Yemen," he said.
He said he did not know if any of the 19 al-Qaida suspects were members of the Ansar al-Islam group in Iraq.
US Secretary of Defense Donald Rumsfeld and others in the Bush administration have previously said the two groups were closely linked.
Aljazeera’s correspondent in Baghdad, Jawad al-Umari, says Bremer’s announcement is an attempt to put pressure on the countries he mentioned, such as Syria and Iran.
“His announcement may also be considered as a call for many countries to send troops to Iraq, as US forces are facing continuous attacks there,” he added.
The US blames Iraqi supporters of former President Saddam Hussein for daily attacks on its troops.
But the Bush administration also says foreign Arab fighters are moving into Iraq, making it a primary front in its so-called War on Terrorism.
Critics of White House policy on Iraq, however, say the US occupation itself has provided the reason why foreigners may be going there to fight.