Jordanian officials say four Iraqis have been arrested for trying to blow up a major hotel in Amman last week.
By Caroline Hawley
BBC correspondent in Amman
The authorities are still giving few details of the attempted attack, but Western officials have confirmed there was a "worrying incident" at a hotel in the middle of last week.
They said it fitted into the pattern of "terrorist activity" they had anticipated after the start of the war on Iraq.
They would not specify the nationality of those involved, but said they had come in from outside the country.
An official at the Jordanian Foreign Ministry said four Iraqis had been arrested.
It is understood the group planted a crude device which failed to ignite fully in the hotel where hundreds of Westerners, particularly journalists, are staying. Western officials say they believe the group may have chosen the hotel because it was a relatively easy target.
The Jordanian authorities had already increased security. Now they have taken further precautions.
British officials say they are planning to strengthen their travel warning for Jordan amid concern of potential attacks across the region as the war continues.