BAGHDAD, Iraq - About 1,000 U.S. Marines and Iraqi troops launched a second offensive Saturday against insurgents in restive Anbar province, this time targeting the marshy shores of a remote lake just north of Baghdad.

Operation Dagger, or Khanjar in Arabic, aims to uncover insurgent training camps and weapons caches in the southern part of the Lake Tharthar area in central Iraq, some 60 miles northwest of Baghdad. The region was the focus of a major campaign in late March that killed 85 insurgents.

"Operation Khanjar is focused on locating hidden weapons caches and denying insurgents sanctuary in the area that is a suspected insurgent and terrorist logistical hub," Marine Capt. Jeffrey Pool said from Ramadi, the provincial capital.

The operation began a day after another 1,000 Marines and Iraqi forces, backed by battle tanks, fought their way into Karabilah, 200 miles west of Baghdad in Anbar province. U.S. fighter aircraft dropped bombs and the tanks fired shells at insurgents holed up inside buildings.

The Marines said Saturday that about 50 insurgents had been killed and 100 insurgents had been captured in that campaign, codenamed Operation Spear.

"Marines and Iraqi soldiers continued operations through the night securing key objectives in and around the city while conducting presence patrols in order to hamper the insurgents movement," Pool added.

During their sweep, four Iraqi hostages were found "beaten, handcuffed and chained to a wall in a bunker located in central Karabilah," he said.

On March 23, U.S. and Iraqi forces killed about 85 militants at a suspected training camp along Lake Tharthar. That raid turned up booby-trapped cars, suicide-bomber vests, weapons and training documents. The insurgents included Iraqis, Filipinos, Algerians, Moroccans, Afghans and Arabs from neighboring countries, officials said.

In early June, Marines sweeping the eastern part of the lake discovered an underground bunker complex in a rock quarry that had recently been used by insurgents and included air-conditioned living quarters and high tech military equipment, including night vision goggles. The military later destroyed the complex and weapons caches.

"The approximate 1,000-man force assigned to Operation Khanjar will search the area for signs of these camps and hidden weapons caches used by insurgents and foreign fighters to launch attacks on Iraqi citizens, soldiers, police and Coalition Forces," Pool said.

Meanwhile, Al-Qaida's No. 2 leader released a new video, broadcast on Al-Jazeera television Friday, in which he disparaged the U.S. concept of reform in the Middle East and said armed jihad is the only way to bring change in the Arab world.

The message by Ayman al-Zawahri appeared to be an attempt by Osama bin Laden's al-Qaida network to co-opt the rising wave of reform movements in the Middle East.

"The removal of the Crusader and Jewish invaders won't occur by peaceful demonstrations," he said in a brief clip shown on the pan-Arab network. "Reform and expelling the invaders from the countries of Islam won't happen except through fighting for God's sake."

The Egyptian was shown in the video sitting before a plain backdrop with an automatic weapon leaned next to him.

He outlined what he called a true program for reform - based on the rule of Islamic law, the end of U.S. and Western domination, and the freedom of the Muslim nation to run its own affairs.

"We cannot imagine any reform while our countries are occupied by the Crusader forces," he said. "We cannot imagine any reform while our governments are being ruled from the American embassies in our countries."