BAGHDAD — As if remembering the good old days, the purported al-Qaida in Iraq militant says he was once in charge of almost 600 fighters before Sunni tribal leaders turned against them, leaving him with a force of 20.

The lament was made in what the military says is the daily diary of an al-Qaida sector leader called Abu Tariq, one of two documents released on Sunday and billed as further evidence that the terror network's operations have been severely curtailed.

"There were almost 600 fighters in our sector before the tribes changed course 360 degrees," Abu Tariq writes, referring to the Sunni tribesmen who have switched sides to fight alongside the Americans. "Many of our fighters quit and some of them joined the deserters ... but things started getting worse ever since."

Rear Adm. Gregory Smith said the documents painted a "narrow but compelling" picture of the challenges facing al-Qaida in Iraq, but he stressed they were by no means defeated.

Underscoring that point, a spate of car bombs and gunmen struck new U.S. allies, police and civilians Sunday in northern Iraq, killing as many as 53 people.

The violence coincided with a visit by Defense Secretary Robert Gates to Baghdad, where he warned that hard choices face Iraq's political leaders on how to stabilize the country despite promising new signs of progress toward reconciliation.

The military said the two documents were discovered by American troops in November as the Sunni movement that began in Anbar province was spreading to Baghdad and surrounding areas.

One was a 39-page memo written by a mid- to high-level al-Qaida official with knowledge of the group's operations in Iraq's western Anbar province; the other a 16-page diary written by another group leader north of Baghdad.

"This does not signal the end of al-Qaida in Iraq, but it is a contemporary account of the challenges posed to terrorists from the people of Iraq," Smith told reporters in Baghdad.

He said the documents are believed to be authentic because they contain details that only al-Qaida in Iraq leaders could know about battlefield movements and tactics. The U.S. military gave reporters partially redacted copies of the full diary but only four pages of the Anbar document, citing security reasons. The documents were provided in their original Arabic as well as the English translation.

In the Anbar document, the author acknowledges a growing weariness among Sunni citizens of militants' presence and the U.S.-led crackdowns against them. He also expresses frustration with foreign fighters too eager to participate in suicide missions rather than continuing to fight.

"The Islamic State of Iraq is faced with an extraordinary crisis, especially in al-Anbar," the author wrote, referring to an umbrella group of insurgents led by al-Qaida.

Smith also quoted the document as saying the group has lost "cities and afterward, villages," adding "we find ourselves in a wasteland desert."

It said U.S.-led forces had learned from their mistakes and improved security had made it harder to transport weapons and suicide belts and forced foreign fighters to go underground because of their distinctive dialects.

The military said the memo was believed to have been written last summer and was intended for the author's superiors.

The diary, seized by U.S. troops south of Balad, was written in autumn 2007 by Abu Tariq, according to the military.

He calls on his fellow militants to show no mercy to the "deserters/traitors," warning they will spread like cancer.

The Sunni tribes' alliance with U.S. forces is credited with helping reduce violence across the country, along with an influx of some 30,000 American troops. A security crackdown that began in Baghdad and surrounding areas a year ago also has driven the militants north.