Iraqi police fought pitched battles with insurgents Sunday as thousands of security forces backed by American troops swept through Baghdad's streets to flush out militants responsible for killing more than 720 people since Iraq's new government was announced in April.

Insurgents lashed back — killing at least 30 people, including a British soldier — and a senior U.S. military intelligence official acknowledged there are few indications they "are packing their bags."

Abu Musab al-Zarqawi's (search) Al Qaeda in Iraq claimed responsibility for nearly all the attacks in Internet statements that could not be independently verified.

In their biggest coup of "Operation Lightning," Iraqi and U.S. soldiers arrested a former general in Saddam Hussein's (search) intelligence service who was also a member of his Fedayeen (search) secret police during a raid in western Baghdad, the scene of some of Sunday's heaviest fighting.

"He now leads the military wings of several terror cells operating in the west Baghdad neighborhood of Ghazaliyah," the military said in its announcement about the former general. It did not release his name or provide further details.

As fighting raged in Baghdad's western neighborhoods, Iraq's freshly minted legislators pounded out their first agreement on the 15 basic articles to guide their new constitution — including democracy, federalism, separation of powers and making Islam the state religion.

The 55-member parliamentary committee has until Aug. 15 to draft the constitution, which must be approved in an October referendum.

"We agreed on 15 articles to be basics for laying down the constitution, including federalism, separation of powers, that people will be the source of those powers, democracy and that Islam would be the official government religion. All of these articles were approved and got unanimous agreement," deputy Saad Jawad Qandil said.

Premier Ibrahim al-Jaafari's Shiite-led government said it would not be deterred by the violence that accompanied the first day of the operation.

"With the escalating operations by security forces, we expect such reactions coming to the surface, but this will have no affect on the operations," said Laith Kuba, spokesman for al-Jaafari.

It was not known how long the operation would last, and its success or failure will be an indication of how long Iraq needs to take control of its own security, a key to any U.S. exit strategy from Iraq.

The first of more than 40,000 soldiers and police, who are being supported by U.S. forces, searched hundreds of vehicles and raided several houses, described as "terrorist dens" in Baghdad's Dora neighborhood, arresting several suspects, army Capt. Ihssan Abdel-Hamza said.

The operation comes after a relentless wave of attacks, mostly carried out by bombers, killed more than 720 people since the April 28 announcement the government, according to an Associated Press count. At least nine militants died in bombings or gunbattles Sunday.

"We have fairly aggressive operations that are being run throughout the Baghdad area," said a senior U.S. military intelligence official who asked not to be named for security reasons. "Basically they are going to sweep Baghdad and make sure that the insurgents are run out of the city."

The official said that despite an early warning that the operation was coming, "We are not seeing any indication that insurgents are packing up their bags."

U.S. military and Iraqi government officials, including al-Jaafari, have said the operation's main target is car bombers, most thought to be foreign fighters recruited in the Gulf region and smuggled into Iraq through Syria.

In the day's biggest battle, about 50 gunmen fired rocket-propelled grenades, mortars and machine guns at a Baghdad police unit in a half-hour battle. The Iraqi forces successfully fought them off, the U.S, military said.

The U.S. military said there were about 143 car bombings in May, a new record. That figure was close to an AP count of over 100 since April 28.

"It is the enemy's precision guided weapon, if you want to look at it that way. It is the way the enemy creates great effects, devastating effects, on the Iraqi civilian population. Because it is the Iraqi civilians that are being killed more by the suicide bombs than by another means of attack in the country," the intelligence official said.

Military officials believe the insurgency is predominantly Sunni Muslim Arab and comprises about 12,000 to 20,000 people, including supporters, while less than 1,000 carry out daily attacks.

They are motivated either by money, the ideology of Saddam's outlawed Baathist party, extreme Islamist radicalism — represented by such groups as al-Zarqawi's — or personal ties, including to family or tribal units taking part in the insurgency.

Cellular in nature, the insurgency is thought to be a broad network that does not have a central command and control structure, according to the official.

Asked if Al Qaeda was behind the network, the officials said "that's the convenient name that everyone wants. I am not sure that in fact is the answer."

Separately, the U.S. military announced the end of a four-day offensive centered on Haditha, 140 miles northwest of Baghdad, aimed at disrupting insurgent activities. At least 14 insurgents were killed and more than 30 suspects detained in the operation, which also left two U.S. Marines dead.

Some of the insurgents in Haditha were believed loyal to al-Zarqawi, whose fate has been the subject of intense discussions this week from Baghdad to the Internet to Washington amid reports that he has been wounded.

Britain's The Sunday Times reported that al-Zarqawi left the country after being wounded in a missile attack and was thought to be in Iran. The paper said it obtained the information from an unidentified senior insurgent commander with close contacts to al-Zarqawi's Al Qaeda in Iraq group. Iran denied al-Zarqawi was there.

U.S. forces said a Marine was killed Saturday when a roadside bomb struck his vehicle near Haqlaniyah, 85 miles northwest of Baghdad. Another soldier who was wounded May 4 died on May 25, it added. At least 1,657 U.S. military members have died since the Iraq war began in March 2003, according to an AP count.

The British soldier died and four others were injured when a British military convoy was attacked in southern Iraq, the Ministry of Defense said in London.