Iraq has become a haven for extremist organizations from throughout the region, experts on extremism say. Numerous places to hide and train, a supportive environment and greater ease with which to attack American interests are some of the reasons they cite.

The experts say that, with its porous security infrastructure, Iraq may well become the region's hotbed of extremism.

Mohammad Saleh, an expert on extremist organizations, is the Cairo bureau chief for the London-based Arabic newspaper Al Hayat. Mr. Saleh says Iraq has become the center of attention for extremist organizations because, he says, those groups look for places lacking security. Iraq, he says, is easy to get into and provides endless places to hide, smuggle weapons, and train.

He believes extremists from places like Afghanistan, Saudi Arabia, Egypt, Sudan, Bosnia, and Albania are looking to enter Iraq in hopes of revitalizing their activities. And, Mr. Saleh says, Iraqis who are angry over the U.S. and British occupation of their country, will likely "embrace" extremism as a chance to force the occupiers out of Iraq.

Mr. Saleh says extremist groups view Iraq as "a last great frontier" in which to wage jihad, or holy war, against the occupying forces. And, he says that, because American troops are so visible in Iraq attacking them is easier.

Hala Mustafa, an expert on extremist groups at the al-Ahram Center for Political and Strategic Studies in Cairo, said Iraq's dominant Shiite population is among those most likely to welcome the support from extremist groups and neighboring governments in making sure America's ideology of democracy does not catch on in Iraq.

"The Shiites in general, they are backed not only by the Shiites or by the Islamists or by the extremists in the Arab world, but I believe they are supported by some other governments and regimes who are not sharing the same ideology or having the same theocratic types," he said. "So, they are using the situation on a very pragmatic basis just to stop the American strategy, or to complicate the work for the Americans in the region."

Ms. Mustafa says Arab nationalists also may try to enter Iraq to battle U.S. and British troops in the name of Arab pride.

Both American and Iraqi officials have said they expect a wide range of Muslim militant groups to enter Iraq and the number of attacks to rise.