Jordanian authorities have found cars carrying explosives that an underground group believed linked to al Qaeda planned to use to attack American interests, a senior security source says.
The source told journalists an unspecified number of cars laden with explosives were found and the suspects who sought to use them had been arrested.
"The group planned attacks on American interests including the embassy and a number of US organisations based in Jordan," he said.
"There is no doubt in our minds they are linked with al Qaeda," he said, adding that the militant network led by Osama bin Laden sought to punish Jordan for supporting Washington's goal of pacifying post-war Iraq.
Senior security officials said earlier this month that cars carrying explosives had been driven into the kingdom from Syria, with which Jordan shares a long desert border.
Officials had said they had uncovered a group planning attacks in the kingdom, arresting some suspects now under interrogation.
Three others got away, and state television has run their pictures, appealing to Jordanians to give the police any information on their whereabouts.
Political analysts and Jordanian politicians say Islamist radicals are incensed over Amman's support for U.S. policies in Iraq.
"They see Jordan as vulnerable and believe any major attack to destabilise the country would weaken American goals in the region and particularly in Iraq," said one security official.
Jordan's close U.S. ties and 1994 peace with Israel are unpopular with many in the conservative kingdom and there is strong support for Islamist militant groups in some areas.
In mid-March, the United States increased its level of alert in Jordan, urging Americans to step up vigilance after receiving information about possible attacks on hotels in the kingdom.
Jordanian authorities have over the last two weeks tightened security at key sites around the capital, including Western embassies, government institutions and key facilities.