The hostages, one Canadian, two French and one South Korean, were among a dozen foreigners seized in an unprecedented wave of abductions and violence in the Palestinian territories on Tuesday amid fury at an Israeli raid on a prison in Jericho.
Canadian teacher Adam Budzanowski, South Korean television correspondent Yong Tae-young and French journalists Caroline Laurent and Alfred Yacobzadeh were delivered into the custody of diplomats in Gaza City.
But unlike others kidnapped on Tuesday, including two Australians, who were held for minutes or hours, the four endured a 24-hour ordeal at the hands of the leftist Popular Front for the Liberation of Palestine (PFLP) whose jailed leader Ahmed Saadat was seized in the raid.
'Collusion'
As security forces braced for further violence, Mr Abbas, who cut short a European tour to rush home to try to restore his battered authority, toured the ruins of Jericho jail where two security guards were killed during the opertion.
"What happened in Jericho was a dreadful crime... Israel had no right to carry out this kidnapping," he said, refering to the seizure by Israel of Saadat and five other incarcerated militants.
Mr Abbas accused British and US monitors, who withdrew from the prison just before it was raided, of complicity with Israel.
Mr Abbas said the Palestinian Authority had been warned that the monitors were set to be withdrawn but were kept in the dark about the timing.
A senior Palestinian official said Mr Abbas would demand that Israel hand back Saadat and five seized militants to their former custody arrangements.
"We will ask the Israeli side to hand back Ahmed Saadat and his colleagues immediately," Palestinian chief negotiator Saeb Erakat said.
But Israel said it was down to Attorney General Menachem Mazuz to decide on the prosecution and trial of the six seized militants, wanted for the 2001 murder of Israeli tourism minister Rehavam Zeevi.
The withdrawal of three British monitors just minutes before Israeli tanks rolled into the prison compound raised fury and charges of collusion that prompted Tuesday's rash of hostage-takings and attacks on British and US offices.
British Prime Minister Tony Blair defended the withdrawal of the monitors, saying it had been forced by concerns for their safety.
"For the past three months we have been warning the Palestinian Authority that the security of these monitors was at risk, that the procedures at the particular detention centre were not adequate and proper," he told British MPs.
But outgoing Palestinian foreign minister Nasser al-Qidwa rejected his explanation. "We do not agree with the assessment that there was any direct threat to the monitors there," he told reporters.
The Israeli government strenuously denied that the raid, a fortnight before a general election, was motivated by political considerations, charging that the Palestinian Authority was on the verge of freeing those suspected of being behind Mr Zeevi's assassination.
"We had no choice but to intervene as no responsible state could allow the murderers of one of its ministers to be at liberty," Defence Minister Shaul Mofaz said.
Security tightened
Amid fury across the Palestinian political spectrum over the raid, the territories ground to a halt under a general strike.
Israeli security forces were on high alert after the PFLP and the Islamist militant group Hamas promised retaliation for the raid.
Hamas spokesman Sami Abu Zuhri said the raid reinforced the group's decision not to recognise Israel and disarm.
"This crime will not pass without a reaction," Mr Zuhri said at a news conference in Gaza with various Palestinian faction members and Hamas prime minister-designate Ismail Haniyeh.
Fearing a potential backlash, security was stepped up across Israel and around the Palestinian territories.
Security was also beefed up around foreign interests, notably British and American offices, after Anglo-US targets suffered the brunt of unrest on Tuesday.