Baghdad, Iraq ? Soldiers, patients and prisoners began voting Monday in national elections, three days ahead of the general population, while insurgents denounced the balloting as a “satanic project” but did not threaten to attack polling stations.

The early voting went ahead despite the sound of detonations rumbling across the capital and at least 15 deaths in ongoing violence.

President Bush offered encouraging words from Washington to Iraqi voters but cautioned that the parliamentary elections “won’t be perfect.”

“Iraqis still have more difficult work ahead, and our coalition and a new Iraqi government will face many challenges,” the president said in a speech in Philadelphia.

Asked about the number of Iraqi casualties from the war and the insurgency, Bush said: “I would say 30,000, more or less, have died as a result of the initial incursion and the ongoing violence against Iraqis.” White House counselor Dan Bartlett later said the number was not an official figure but that Bush was simply repeating public estimates reported in the media.

In a rare joint statement, al-Qaida in Iraq and four other Islamic extremist groups denounced the election as a “satanic project” and said that “to engage in the so-called political process” violates “the legitimate policy approved by God.”

The groups vowed to “continue our jihad (holy war) … to establish an Islamic state ruled by the book (the Quran) and the traditions of the Prophet Muhammad.”

Captain Firas Al-Timimi of the Iraqi army displays his ink stained finger Monday at Basra Palace in Basra, Iraq, after casting his vote in the country's election at a separate location earlier in the day.

However, the statement contained no clear threat to disrupt voting as in the run-up to the Jan. 30 election and the Oct. 15 referendum on the constitution.

The authenticity of the statement could not be verified, but it appeared on a Web site that often publishes extremist material.

The absence of a clear-cut threat could reflect the growing interest among Sunni Arabs, the foundation of the insurgency, to take part in the election. The Sunni decision to boycott the January ballot left parliament in the hands of Shiites and Kurds – a move that increased communal friction and cost the Sunnis considerable influence in drafting the constitution.

In the first day of early voting, about 250,000 Iraqis – soldiers, police, hospital patients and prisoners – cast ballots, according to election official Abdul-Hussein Hendawi. Iraqi television aired footage showing inmates in orange jumpsuits depositing their ballots in jailhouse boxes.

The U.S.-led multinational force said 90 percent of all eligible detainees held in facilities under its control participated in the vote. It did not release the number represented by that percentage. Suspected insurgents held in detention but not convicted were eligible to vote, officials said.

Deposed leader Saddam Hussein, who is jailed and facing trial for the deaths of more than 140 Shiites in 1982, also could vote, but it was not known if he did.

Abroad, an estimated 1.5 million expatriate Iraqis will begin voting today over a two-day period in polling centers in 15 countries including the United States.

Most of the 15 million registered voters go to the polls Thursday.

U.S. and Iraqi officials have expected an upsurge in insurgent violence as the election approaches.

A U.S. soldier was killed Monday in a bombing in Baghdad, and another American soldier attached to the Marines died the day before in a suicide bombing west of the capital near the city of Ramadi, the U.S. command said.