BAGHDAD (AP) A son of Libyan leader Moammar Gadhafi is behind a group of foreign and Iraqi fighters responsible for this week's devastating explosion in northern Iraq, a security chief for Sunni tribesmen who rose up against al-Qaida said Saturday.

At least 38 people were killed and 225 wounded last Wednesday when a huge blast destroyed about 50 buildings in a Mosul slum. The next day, a suicide bomber killed the provincial police chief and two other officers as they surveyed the blast site.

Col. Jubair Rashid Naief, who also is a police official in Anbar province, said those attacks were carried out by the Seifaddin Regiment, made up of about 150 foreign and Iraqi fighters who slipped into the country several months ago from Syria.

Naief said the regiment, which is working with al-Qaida in Iraq, was supported by Seif al-Islam Gadhafi, 36, the eldest son of the Libyan leader.

"I am sure of what I am talking about, and it is documented," Naief said, adding that he was "100 percent sure" of the younger Gadhafi's role with the terror group.

A man who answered the phone at Gadhafi's office in Tripoli said Gadhafi was not immediately available for comment on the accusation.

Naief told The Associated Press his information about the Seifaddin Regiment and the younger Gadhafi's purported role came from "reliable sources" maintained by his Anbar Awakening Council within the ranks of al-Qaida in Mosul and elsewhere.

He said the information was passed to the U.S. military two or three months ago.

"They crossed the Syrian border nearest to Mosul within the last two to three months," Naief said of the Seifaddin Regiment. "Since then, they have taken up positions in the city and begun blowing up cars and launching other terror operations."

The Anbar Awakening Council is an alliance of Sunni tribes in the western province that turned against al-Qaida and began working with U.S. forces. The council is credited with the sharp drop in violence in Anbar, once the main base for the insurgents.

Many of the council's fighters are believed to have been insurgents themselves until they began receiving money from the Americans to turn their guns on their former extremist allies.

The U.S. military did not immediately respond to an e-mail request for comment about Naief's claim.

Last Monday, however, The Washington Post reported that U.S. military commanders believed they had underestimated the role of North Africans in the ranks of foreign fighters and suicide bombers in Iraq.

The newspaper quoted U.S. military officials as saying that 19 percent of the foreign fighters come from Libya. Overall, North Africans account for 40 percent of the foreign fighter ranks, the newspaper said.

Seif al-Islam, however, seems an unlikely figure as a sponsor of terrorism. Touted as a reformer, the younger Gadhafi has been reaching out to the West to soften Libya's image and return it to the international mainstream.

Known in Libya as "The Engineer," he won praise last year for helping release five Bulgarian nurses and a Palestinian doctor who were jailed in Libya for allegedly infecting Libyan children with HIV.

Educated at a British university and fluent in English, German and French, he also has gained exposure as head of the Gadhafi International Association for Charitable Organizations, a non-governmental network concerned with issues like human rights and education.

Naief did not explain why the younger Gadhafi would be sponsoring the group of fighters. Seif Gadhafi, however, was quoted by the Austrian Press Agency last year as warning Europeans against more attacks by radical Islamists.

"The only solution to contain radicalism is the rapid departure of Western troops from Iraq as well as Afghanistan, and a solution to the Palestinian question," Gadhafi was quoted as saying.

This week's blasts have drawn attention to the security situation in Mosul, which U.S. commanders describe as the last major urban center with a significant al-Qaida presence since the terror network has been driven from its strongholds in the capital and Anbar province.

The U.S. military is relatively thin across northern Iraq and has signaled no immediate plans to shift American troops from key zones in and around Baghdad.

On Friday, however, the government said it would dispatch several thousand more Iraqi security forces to Mosul in a "decisive" bid to drive al-Qaida in Iraq from the city.

Defense Minister Abdul-Qadir al-Obeidi told reporters Saturday that the first reinforcements would arrive in the city within 24 hours.

Mosul and surrounding Ninevah province have about 18,000 policemen, but only about 3,000 operate in the city of nearly 2 million, according to police spokesman Saeed al-Jubouri.

The U.S. wants to keep Iraqi security forces in the lead as a major test of Washington's long-range plans, which seek to keep a smaller American force in Iraq as backup for local soldiers and police.

Associated Press writers Muheiddin Rashad, Sameer N. Yacoub and Hamed Ahmed contributed to this report.