BAGHDAD, Iraq (AP) – The new leader of Al Qaeda in Iraq purportedly said Thursday in an audio message posted online that more than 4,000 foreign terrorists have been killed in Iraq since the American-led invasion in 2003 – the first apparent acknowledgment from the insurgents about their losses.

The message also called for experts in the fields of “chemistry, physics, electronics, media and all other sciences – especially nuclear scientists and explosives experts” to join the terror group’s holy war against the West.

“We are in dire need of you,” said the man, who identified himself as Abu Hamza al-Muhajir – also known as Abu Ayyub al-Masri – the leader of Al Qaeda in Iraq. “The field of jihad (holy war) can satisfy your scientific ambitions, and the large American bases (in Iraq) are good places to test your unconventional weapons, whether biological or dirty, as they call them.”

It was unclear why Mr. al-Masri would advertise the loss of the group’s foreign fighters, but martyrdom is revered among Islamic fundamentalists, and could be used as a recruiting tool. The Arabic word he used, “muhajer,” indicated he was speaking about foreigners who joined the insurgency in Iraq, not coalition troops.

“The blood has been spilled in Iraq of more than 4,000 foreigners who came to fight,” Mr. al-Masri purportedly said on the 20-minute tape. The voice could not be independently identified.

The statement followed the release of a U.N. report Wednesday that said fewer foreign fighters have been killed or captured in Iraq in the last few months, “suggesting that the flow has slackened.” The report, which cited several intelligence and security agencies, also said some fighters had expressed dissatisfaction they were asked to kill fellow Muslims rather than Western soldiers and that the only role for them was to be suicide bombers.

Analysts said Mr. al-Masri’s statement appeared aimed at burnishing the group’s image.

“It’s showing the level of dedication to their cause, the level of sacrifice jihadists are making. … It’s almost showing a sense of strength and purpose to other people around world who might be thinking about joining the fight,” said Ben N. Venzke, director of IntelCenter, an America-based group that provides counterterrorism information to the American government and media.

In the audio message, Mr. al-Masri also offered amnesty to Iraqis who cooperated with their country’s “occupiers,” calling on them to “return to your religion and nation” during the Muslim holy month of Ramadan, which Sunnis began observing in Iraq on Saturday and Shiites on Monday.

“We will not attack you as long as you declare your true repentance in front of your tribe and relatives,” he said. “The amnesty ends by the end of this holy month.”

He urged insurgents to capture Westerners so they could be traded for the imprisoned Egyptian sheik Omar Abdel-Rahman, who was convicted in 1995 of conspiring to blow up New York landmarks.

“I appeal to every holy warrior in the land of Iraq to exert all efforts in this holy month so that God may enable us to capture some of the Western dogs to swap them with our sheik and get him out of his dark prison,” the voice on the tape said.

Mr. al-Masri, a Sunni Muslim, is believed to have succeeded Abu Musab al-Zarqawi, who died in an American airstrike north of Baghdad in June.

Mr. al-Masri appeared last week in a Web video apparently killing a Turkish hostage in Iraq. The video, initially released in 2004, was believed to be the first of Mr. al-Masri to be released since he took control of the militant group.

Thursday’s audio recording appeared on a Web site that frequently airs Al Qaeda tapes and messages. A banner posted there Wednesday said Al Qaeda No. 2 Ayman al-Zawahri would soon release a new message about the pope, President Bush and Sudan’s troubled Darfur region.

Meanwhile, police found 40 more bodies in the capital, and bombings and shootings killed at least 21 people in a spike of violence with the onset of Ramadan.

A car bomb exploded near a restaurant in central Baghdad, killing five people and wounding 34, police said. Many of the injured had serious burns and some were not expected to survive, police Lt. Ali Mohsen said at the Kindi Hospital.

Although the Muslim fasting month of Ramadan is under way, some Iraqis – including Christians – are not abstaining from eating meals during daytime hours.

Two Iraqi soldiers were killed and 10 more injured when a suicide car bomb slammed into a checkpoint in northeast Baghdad, police said. The attack came in the Shaab neighborhood, one that just been cleared by American and Iraqi troops as part of a security drive in the capital.

The bodies of 40 men, more apparent victims of sectarian death squads, have been found dumped in eastern and western Baghdad in the past 24 hours, police said. All showed signs of torture, had been shot, and had their hands and feet bound, police Lt. Thayer Mahmoud said.

Gunmen killed seven people, including five policemen and a woman, in different locations in the province of Diyala just north of Baghdad, police said. Six militants were killed in a shootout between Iraqi soldiers and a truckload of gunmen southwest of the capital, officials said.

Iraq’s government warned residents that it will soon restrict vehicle access into the capital as part of a security crackdown targeting militants and death squads.

The violence also came amid reports from a number of senior coalition military officials that a large and powerful militia run by radical Shiite cleric Muqtada al-Sadr has been breaking apart into freelance death squads and gangs – some of which are being influenced by Iran.

Mr. al-Sadr’s Mahdi army is one of the largest and most powerful militias in Iraq, along with the Badr Brigades, which were once the military wing of Iraq’s largest Shiite political group – the Supreme Council for the Islamic Revolution in Iraq.

“There are fractures politically inside Sadr’s movement, many of whom don’t find him to be sufficiently radical now that he has taken a political course of action,” said a senior coalition intelligence official who spoke to reporters in Baghdad on condition of anonymity because he was not permitted to speak publicly on intelligence issues.

The official added that “there have been elements. I can think of about at least six major players who have left his organization because he has been perhaps too accommodating to the coalition.”

On Sept. 22, Mr. al-Sadr urged his followers not use force against American troops, saying “I want a peaceful war against them and not to shed a drop of blood.

Mr. al-Sadr’s ability to control his militia is important both to the American military and an Iraqi government seeking to control and disarm militias and death squads blamed for thousands of sectarian killings in recent months.

Iran has also sought to influence rogue or splinter elements that have broken away from the Mahdi army while it is still able to, the senior intelligence official said.