The militant Popular Front for the Liberation of Palestine (PFLP) has warned of conflict over the arrest of its leader, Ahmad Saadat, by the Palestinian Authority.

"The authority should know that what it did will put it in full confrontation with all the national and Islamist factions without exception," PFLP spokesman Maher al-Tahir said in a statement.

We cannot find the words to express our rage and condemnation of [Ahmad Saadat's] arrest

Joint statement, Palestinian militant groups

PFLP officials have said Mr Saadat - wanted by Israel in connection with the assassination of its tourism minister last October - was arrested in the West Bank town of Ramallah on Tuesday evening.

Hundreds of Palestinians - some carrying PFLP flags - took to the streets of the West Bank on Wednesday in protest at Mr Saadat's arrest.

The militant Islamic group Hamas said Wednesday it would resume attacks "in all its forms, including martyrdom [suicide] attacks".

Last month, the movement said it was suspending suicide attacks in Israel and mortar attacks on Jewish settlements in the interests of Palestinian national unity.

It also warned the Palestinian leadership: "If the Palestinian Authority continues in this path it will be digging its own grave," Reuters news agency reported.

Body found

In a separate development, a body with gunshot wounds was found in an Israeli car in the West Bank near the northern Palestinian city of Nablus on Wednesday, Israeli security sources said.

The circumstances of the death, a day after Palestinian gunmen killed two Jewish settlers, were not immediately clear, but security sources said the body was that of an Israeli Arab from Jerusalem.

Israel says it wants proof that Palestinian police have arrested Mr Saadat.

"Until I see him behind bars, I won't believe it," Raanan Gissin, an adviser to Israeli Prime Minister Ariel Sharon, told Reuters.

The PFLP says Saadat was arrested after being tricked into a meeting with the Palestinian Authority

"We've been disappointed so many times and fed up with so many announcements that they've arrested someone."

The assassination of Tourism Minister Rehavam Zeevi sparked an Israeli blockade of Ramallah, hemming Palestinian leader Yasser Arafat into the West Bank town.

Israel said it would not allow Mr Arafat to leave Ramallah until Mr Saadat and other suspects in Mr Zeevi's murder were arrested and extradited to Israel.

Mr Saadat's deputy, Abdel Rahim Mallouh, said Mr Saadat had been detained during a meeting with a Palestinian Authority official.

"This is a political action, which has very dangerous political consequences," Mr Mallouh was quoted as saying by the Associated Press.

"We consider this a response that they have accepted all American pressure and Israeli demands," he said.

West Bank shootings

News of the arrest followed the killing on Tuesday of two Israelis by gunmen in separate incidents in the West Bank.

An Israeli woman was killed and a passenger injured in a shooting outside the Jewish settlement of Givat Zeev, local security officials reported.

Hours earlier, the body of a 72-year-old Israeli-born American, Avi Boaz, had been pulled from a bullet-ridden car in the Palestinian town of Beit Sahour near Bethlehem.

Tuesday's attacks - and the killing of an Israeli soldier on Monday - follow the suspicious death of Raed al-Karmi, the head of an armed faction linked to Yasser Arafat's Fatah movement.

Israeli security sources have told the BBC that Israeli agents were behind the blast although the government has not officially admitted responsibility for his death.