Syrian militants linked to al Qaeda's leader in Iraq, Abu Musab al-Zarqawi, were behind last week's rocket attack on US warships in the Red Sea port of Aqaba, Jordanian security officials said on Tuesday.
Zarqawi's Sunni Muslim group claimed responsibility for Friday's attack, in which the rockets missed their targets, but hit a warehouse and a hospital, killing a Jordanian soldier, and struck the Israeli port of Eilat.
An Internet statement said those who had carried out the strikes had "withdrawn ... and returned safely to their base".
The Jordanian officials identified the suspects as an Iraqi named Mohammed Hameed Hassan, also known as Abu Mukhtar, and a Syrian named Mohammed Hassan Abdullah al-Sahli and his two sons.
The officials, who asked not to be named, said Sahli had been part of an al Qaeda sleeper cell in Amman. He was arrested shortly after his sons, Abdullah and Abdul-Rahman, fled across the border to Iraq with Hassan on Friday.
They said the Syrians had used forged Iraqi passports to enter Jordan, a tightly policed pro-Western kingdom where militant attacks are rare.
Another security source said the four-member group had received direct orders from Zarqawi, a Jordanian who has led a campaign of bombings and kidnappings in postwar Iraq.
The attack was the most serious on US targets in Jordan since the 2002 killing of American diplomat Lawrence Foley in Amman. A Jordanian court has convicted Zarqawi in absentia for Foley's shooting and sentenced him to death.
Amman has received several warnings in recent months that al Qaeda planned to attack the port of Aqaba, which handles many supplies for US forces in Iraq, security sources said.
They said the three missiles fired in Friday's attack were among seven Katyusha rockets smuggled into Jordan from Iraq by car two weeks earlier. The other four were found abandoned.
A Jordanian source said Amman was concerned about signs that Syria had become a conduit for anti-US fighters heading to Iraq - as US officials complain - but said there was no proof the Damascus government condoned such activities.