Palestinian President Mahmoud Abbas has appointed three new security chiefs as part of a major reform aimed at cracking down on widespread corruption.
Mr Abbas knows sweeping reforms could make him unpopular
Top commanders chosen by the late Yasser Arafat have been removed.
Hundreds of their men are leaving under a retirement plan announced earlier this month, under which officers have to retire at the age of 60.
The move is likely to please the US and Israel, which had been urging sweeping changes to the security forces.
The Palestinian security apparatus has long been seen as weak and inefficient in reining in militants and maintaining law and order.
Among those removed is also Moussa Arafat, a cousin of the former PLO leader, who headed the national security forces in the Gaza Strip.
Brigadier General Suleiman Helles was been appointed to replace him.
The former heads of the Palestinian police and of the intelligence services, have been replaced, too.
The new intelligence chief is Tareq Abu Rajab, while Ala Hosni has been named as the new police chief.
Mr Rajab, the former deputy intelligence chief, played an important role in a crackdown on the militant group Hamas.
He was seriously injured in a driveby shooting in which Palestinian militants killed two of his bodyguards.
The names of the three new top security chiefs, which were formally announced on Saturday, had leaked earlier during the week.
The reform is an attempt at streamlining nine security branches which have been in competition with each other in the past.
In carrying out his reforms, Mr Abbas has to be careful not to alienate influential figures in the Fatah movement which have played prominent roles in leading the security forces in the past.
Mr Arafat and Amin al-Hindi, the former intelligence chief, will become special advisers to the president, a senior aide, Tayeb Abdel-Rahim, was reported by Reuters news agency as saying.