NICOSIA, Cyprus (AP) _ An assassination attempt on Saddam Hussein has shaken his regime due to suspicions that some of his closest associates were involved, say well- informed sources who were recently in Iraq.

At least 60 senior military, police and government officials have been detained and interrogated in an investigation led by Saddam's youngest son, Qusai, 28, who heads his father's personal intelligence apparatus, they said.

Saddam himself and his eldest son, Odai, also have been involved in the interrogations, the sources said.

Unconfirmed reports said 20 army officers, some senior, have been executed since the Sept. 24 bombing attack. The bomb was set off as Saddam's motorcade passed on the way to a meeting only a few top officials knew about, the sources said.

The sources, Arab businessmen and Western diplomats, spoke to The Associated Press in Cyprus, Lebanon and Jordan on condition of anonymity. Some feared reprisals if their identities were revealed.

The sources said members of Saddam's inner circle have been questioned, although none are known to have been detained.

They included Vice President Taha Yassin Ramadan, Deputy Prime Minister Tariq Aziz, Defense Minister Ali Hassan al-Majid and Rashad Amin, Saddam's adviser and chief bodyguard, the sources said. Aziz is Iraq's international negotiator, Al-Majid is Saddam's cousin and one of his closest aides, and Amin is the president's brother-in-law.

The sources said the attack sent shock waves through the regime and undermined confidence in Saddam's security.

They said Saddam's assailants detonated a roadside bomb in Baghdad's northeastern outskirts as his motorcade passed. The 56-year-old leader, riding in a black, armored Mercedes-Benz limousine was not hurt, but one of his bodyguards was wounded, they said.

Saddam was on his way to a hastily arranged meeting with senior aides, including Ramadan, Aziz, al-Majid and Amin, the sources said. Only a handful of officials knew about the meeting, they said.

The attack resulted in what several sources described as unprecedented security around the Iraqi leader.

Since he took power in 1979, Saddam has survived many assassination and coup attempts, thanks mainly to his pervasive, well-armed security apparatus.

Iraqi opposition sources said their groups were not involved in the attack, supporting the theory that the plot was hatched within the regime.

In recent weeks, Iraqi sources have reported increasing friction within Saddam's family, the Tikriti clan's inner circle.

Many Sunni Muslims, a minority in Iraq but long a pillar of the ruling apparatus, are also increasingly disenchanted after three years of U.N. trade sanctions.