Saudi security agents have captured four suspected terrorists accused of plotting attacks, but three others escaped after a shootout with authorities, an official news report said Wednesday.

The Saudi Press Agency issued a statement by an unidentified Interior Ministry official saying the crackdown on two terrorist cells had foiled attack plots that were in the early planning stages.

The official said agents, acting on a tip, arrested a member of a cell in al-Qassim, 220 miles northwest of the capital, Riyadh (search). The suspect said three of his colleagues were hiding in a nearby farm.

Police raided the farm Wednesday. Two security men were wounded in a firefight during a car chase with the three suspects, who took a bystander's car at gunpoint and escaped.

Agents uncovered arms and large quantities of chemicals used to make explosives on the farm, the official said. Al-Qassim has long been a hotbed of extremism.

An earlier tip identified a cell of three people in a desert area east of Riyadh, the official said. Security officials raided their hideout Sunday and arrested all of them.

The statement said the arrests in recent days involved two cells and did not say whether the two groups were in contact or cooperation with each other. The official did not identify the men in custody.

"Thanks to God, the security apparatus in the Interior Minister discovered some cells in their early planning stages of terror operations," said the official quoted on the Saudi Press Agency. "Most of the cell members were arrested and the weapons and banned material in their possession confiscated."

The targets of the terror plots were not identified. The American Embassy in Riyadh posted a message on its Web site Monday warning U.S. citizens that newly obtained information suggests that "known terror operatives" have identified outdoor sites frequented by Westerners.

The embassy message said it was unknown if the new intelligence was linked to possible terrorist attacks.

U.S. officials have praised Saudi Arabia (search) for unprecedented cooperation in the anti-terror fight after bombing attacks in Riyadh on May 12 killed 35 people, including nine Saudi attackers. Saudi officials have said the 19 suspects in the bombings were in contact with Al Qaeda (search), the group blamed for the Sept. 11 attacks in the United States.