Palestinian President Mahmoud Abbas has named three new heads for the security forces and forced hundreds of their men into retirement, pushing aside top commanders in Yasser Arafat's old guard.
The shake-up brings Mr Abbas closer to meeting Israeli and US demands for reform of corruption-plagued security forces, also criticised by ordinary Palestinians for failing to maintain law and order.
Brigadier General Suleiman Helles was named national security forces commander to replace Moussa Arafat, a Gaza strongman who is a cousin of the late Palestinian leader. Mr Abbas replaced Palestinian intelligence chief Amin al-Hindi with his deputy, Tareq Abu Rajab.
Ala Hosni was named as the new police chief.
Hundreds of other security men were also forced out under a new law requiring forces personnel to retire at 60, including dozens of senior officers, among them 11 with the rank of Major General.
"Today they are giving a wonderful new example by the smooth and civilised transfer of responsibility and authority," said senior Abbas aide Tayeb Abdel-Rahim in a statement.
Mr Abbas, elected in January, is walking a political tightrope in carrying out the reforms.
While he is under pressure at home and abroad for reforms that could be vital to Middle East peacemaking, Mr Abbas needs to avoid alienating powerful leaders in the faction-ridden Fatah movement who have long held sway over security forces.
The United States and Israel had been pushing for changes to more than a dozen security forces that were often in competition with each other. Palestinians complained that disorder was growing despite the tens of thousands of security forces personnel, who were widely seen as incompetent and often corrupt.
Mr Abbas has guaranteed good pensions for the departing officers, which could help reduce opposition to the forced retirements, officials said.
Abdel-Rahim said that two of the outgoing security men, Moussa Arafat and Hindi, had been re-assigned as special advisers to the president.