BAGHDAD -- An al-Qaida front group in Iraq on Sunday confirmed the killing of its two top leaders but vowed to keep up the fight despite claims by U.S. and Iraqi officials that the deaths could be a devastating blow to the terror network.

The defiance came in a statement released a week after the group's leaders -- Abu Omar al-Baghdadi and Abu Ayyub al-Masri -- were killed in a raid by Iraqi and U.S. security forces on their safe house near Tikrit, north of Baghdad.

"After a long journey filled with sacrifices and fighting falsehood and its representatives, two knights have dismounted to join the group of martyrs," the statement said. "We announce that the Muslim nation has lost two of the leaders of jihad, and two of its men, who are only known as heroes on the path of jihad."

The four-page statement by the Islamic State of Iraq was posted on a militant website early Sunday.

It concluded: "The war is still ongoing, and the favorable outcome will be for the pious."

The Islamic State of Iraq is an offshoot of al-Qaida in Iraq. Al-Baghdadi was its self-described leader and was so elusive that at times U.S. officials questioned whether he was a real person or merely a composite of a terrorist to give an Iraqi face to an organization led primarily by foreigners.

Al-Masri, a weapons expert who was trained in al-Qaida camps in Afghanistan in the late 1990s, was the shadowy national leader of al-Qaida in Iraq.

Their deaths were triumphantly announced April 19 by Iraqi Prime Minister Nouri al-Maliki. U.S. Vice President Joe Biden called the killings a "potentially devastating blow" to al-Qaida in Iraq.

But four days later, officials think al-Qaida struck back, bombing mosques, shops and the office of an influential Shiite cleric, killing 72 people in Iraq's bloodiest day of the year so far. Homes of police also were bombed. Al-Maliki said the insurgents were fighting back after the deaths of their two leaders.

The new statement did not mention Friday's bombings, and no group has claimed responsibility for them yet.

"Commit to what those two leaders stood for," the statement reads. "Transform the blood of those two leaders into light and fire -- a light which will illuminate the path before you and facilitate your ability of speech, and a fire against the enemies of the creed and the religion."

Al-Qaida in Iraq has proved resilient in the past, showing a remarkable ability to change tactics and adapt -- most notably after its brutal founder, Abu Musab al-Zarqawi, was killed nearly four years ago in a U.S. airstrike. Still, it is widely thought that the group was far stronger then and likely would have a harder time now replenishing its leadership and sticking to a timetable of attacks.

Meanwhile, the police chief in Hawija, 150 miles north of Baghdad, said troops raided the nearby town of al-Safra and arrested Burhan Mahmoud Mohammed, a local leader of the Islamic State of Iraq.

Col. Fatah al-Khafaji told The Associated Press that troops acted on intelligence but did not indicate exactly where the information came from. Iraqi officials have said the investigation into al-Baghdadi and al-Masri, especially the arrest in March of a senior al-Qaida official, also has led them to a number of other leaders associated with the insurgency.