The head of Iraq's nuclear programme Jaffar al-Jaffar surrendered while Saddam Hussein's half-brother and former adviser Watban Ibraham al-Hasan was detained as he attempted to enter Syria.

NBC

reported that Jaffar - who was heading the nuclear programme for two years - did not surrender to US authorities but sources said US would have the opportunity to speak with him.

However, it was not clear which government he had surrendered to.

Jaffar could provide valuable insight into Iraq's nuclear programme, including information o­n where material might be located, as well as the names of scientists who may have been involved in the programme.

Meanwhile Watban Ibrahim had been captured by local tribesmen and turned over to coalition forces.

According to the report, Watban Ibrahim was dismissed from his position as interior minister in 1995 and made a presidential adviser.

He had been estranged from the regime because Saddam considered him to be a threat.

Both the leaders were among the 55 top Iraqi officials featured o­n Pentagon's deck of playing cards which have been distributed to US troops.

On Saturday, Saddam's science adviser surrendered Lt Gen Amer al-Saadi surrendered to US military authorities.

He insisted that Iraq had no weapons of mass destruction, the catalyst for the US to wage the war against the regime.

POWs released

In another development, seven US prisoners of war were released near Tikrit yesterday.

A CNN report said the POWs were recovered by marines who had been sent into Samarra to keep traffic from interfering with an armoured column approaching the battle.

An Iraqi policeman approached the marines and asked if they had come for the prisoners. He led the marines to a nearby building, where they found the seven Americans guarded by at least o­ne Iraqi soldier.

US Central Command identified the seven as Spc Joseph Hudson, Sgt James Riley ( third left ), Spc Shoshana Johnson, Spc Edgar Hernandez and Pfc Patrick Miller - members of a convoy from the US army's 507th Maintenance Company that was ambushed o­n March 23 near Nasiriya - and chief warrant officers Ronald Young Jr ( third right ) and David S Williams ( second left ), pilots who were captured March 24 after their Apache helicopter gunship went down south of Baghdad.

In Baghdad, US Marines reportedly exchanged fire early today with snipers in a building near the Palestine Hotel, where many Western journalists are housed.

For more than two hours, beginning just before 1.30am (6.30am Malaysian time), Marines staked out positions along Firdos Square, occasionally firing rounds of ammunition and sending up flares to light the area.

Tikrit battle

Meanwhile, Reuters reported that US marines in armoured vehicles closed in o­n Tikrit today after a fierce battle against Iraqi loyalists in the outskirts of Saddam Hussein's hometown.

A task force of the First Marine Expeditionary Force, supported by helicopters and F-18 warplanes, attacked remnants of the Iraqi Republican Guard and paramilitary fighters o­n the southern edge of Tikrit o­n yesterday as they thrust toward the city center.

Several Iraqi tanks were destroyed and at least 15 Iraqis were reportedly killed in the firefight.

Tikrit is dominated by the clan of Saddam, who was born in a nearby village. US military planners have suggested that troops loyal to the deposed Iraqi leader might make a last stand there.

However, armed men in Tikrit told al-Jazeera that tribal leaders were negotiating a cease-fire with U.S. forces and Iraqi troops and paramilitaries had left.