Updated

Saddam Hussein loyalists are fighting an increasingly organized "guerrilla-type campaign" against U.S. troops, and terror groups are reviving, too, the commander of U.S. forces in Iraq says.

Highlighting the danger, American forces found a cache of about 4 tons of military explosives in central Iraq Thursday, a senior official at the Pentagon said. Troops found the stash of C-4 explosives about 30 miles southwest of Baghdad after being tipped by Iraqis, the official said, speaking on condition of anonymity.

More than 1,000 Iraqis have been arrested in the U.S. military's latest sweep for anti-American fighters, called Operation Soda Mountain (search), which began over the weekend, the official said. Those arrested include about 50 people who may be ringleaders of some of the attacks against American troops, the official said.

Gen. John Abizaid (search) said the threat was nothing that the troops couldn't handle. "They're not driving us out of anywhere," the four-star general said Wednesday.

Still, Abizaid's use of the term "guerrilla warfare" was a striking departure for a top military leader. As recently as last week, Defense Secretary Donald H. Rumsfeld and other Pentagon officials refused to use the term, saying attacks on U.S. forces were too sporadic and disorganized to qualify as a guerrilla campaign.

Abizaid credited attackers with improved organization, tactics and financing as he suggested American soldiers may face deployments of a length seldom seen since the Vietnam War.

However, he pledged that soldiers in the Army's longest-serving unit in Iraq, the 3rd Infantry Division, would be on their way home by the end of September. Other U.S. troops will be given a firm homecoming date.

"It's very, very important to all of us to make sure that our soldiers, sailors, airmen and Marines know when they're coming home," Abizaid said at a Pentagon news conference.

He suggested that comments by a few soldiers in a television interviews — including one who said he wanted to ask Rumsfeld to resign — simply show the frustration of young people who are ready to go home.

"Every now and then we've got to look at our young people and understand why they said what they said, and then do something about it," Abizaid said.

He declined to speculate on whether those soldiers could face punishment but added: "None of us that wear this uniform are free to say anything disparaging about the secretary of defense, or the president of the United States."

Before they go home, those troops undoubtedly will face more attacks from former members of Saddam's Baath Party and from terrorist groups who want to derail Iraq's transition to democracy, Abizaid said. He spoke on a day when attackers killed the pro-American mayor of a northwestern Iraqi town and a U.S. soldier in Baghdad.

Though Rumsfeld has avoided characterizing the situation as "guerrilla warfare", Abizaid said Wednesday it was the proper term.

"It's low-intensity conflict in our doctrinal terms, but it's war however you describe it," said Abizaid, who took over last week as head of U.S. Central Command.

Midlevel Baath Party (search) operatives have organized themselves into cells of perhaps 10 people. With some regional coordination and financing, those cells plan attacks on American forces with improvised bombs, machine guns, rocket-propelled grenades and other weapons, Abizaid said.

Terrorist groups pose another threat to American forces, he said.

Those groups operating inside Iraq include Ansar al-Islam, an Al Qaeda-linked organization whose camp in northern Iraq suffered devastating attacks from U.S. forces in the early stages of the war in Iraq. Ansar al-Islam appears to be regrouping in Iraq, possibly aided by members coming from Iran, Abizaid said.

Other non-Iraqi fighters have ideological sympathies for Al Qaeda leader Usama bin Laden, if not orders from him to attack Americans, he said.

Wednesday's unsuccessful missile attack on a C-130 cargo plane landing in Baghdad was the second in as many weeks, Abizaid said. U.S. commanders remain worried about the threat from shoulder-fired anti-aircraft missiles, the general said.

Abizaid said he was recently a passenger in a C-130 over Iraq when the crew swerved the plane and fired flares to avoid a possible missile launch.

"These were guys from the Oklahoma National Guard, and they actually thought it was fun. I was terrified," Abizaid said.

About 148,000 U.S. troops are in Iraq, bolstered by an additional 12,000 or so from coalition countries, mainly Britain and Poland. The number of troops in Iraq is about right for the next several weeks, at least, Abizaid said.

"If the situation gets worse, I won't hesitate to ask for more," he said.