YATMA, West Bank, Sept 8 (Reuters) - Israeli settlers sprayed graffiti on a mosque and torched Palestinian cars in the occupied West Bank on Thursday, angered by Israel's demolition of structures at an unauthorised outpost, Palestinian officials said.

"We condemn these attacks and also the Israeli government for allowing this to happen," Palestinian Authority spokesman Ghassan Khatib said, urging the international community "to provide our people with protection".

The name of the settler-outpost, Migron, where security forces tore down three structures on Monday, was painted on an exterior wall of the mosque in the village of Yatma, along with the Hebrew acronym for the words "Price Tag".

Palestinian officials said two cars were set ablaze in a nearby village and several olive trees uprooted.

Some settlers and their supporters have used the "Price Tag" slogan to signify payback for any Israeli curbs on settlement in the West Bank, territory Israel captured in a 1967 war.

Migron was built without Israeli government permission and a court ordered the demolitions, which were followed hours later by an arson attack on a mosque in the West Bank village of Qusra, an incident condemned by Prime Minister Benjamin Netanyahu.

On Wednesday, an Israeli army base in the West Bank was vandalised and pro-settler graffiti daubed on its walls, the first such incident at a military installation.

Israeli police spokesman Micky Rosenfeld said a special task force had been set up to investigate the attacks and apprehend suspects, although no arrests had yet been made.

The governer of the Palestinian city of Nablus near Yatma ordered formation of local vigilante groups in villages neighbouring settlements in the area to protect Palestinians and their property from more settler attacks.

Governor Gibril al-Bakry said his orders for the formation of "popular defence committees" followed "the serious escalation in settler attacks", the official Palestinian news agency WAFA reported.

It was the first sign of an organised Palestinian response to the settler violence.

Palestinians and human rights groups have accused Israeli authorities of turning a blind eye to settler violence against Palestinians and say assailants are rarely caught or prosecuted.

Some 500,000 Israelis live in the West Bank and East Jerusalem, which was also captured in the 1967 conflict. About 2.5 million Palestinians reside in the two areas.

Palestinians hope to establish a state in the West Bank and Gaza Strip. T he Israeli government says a return to the pre-1967 frontier would leave Israel with an indefensible border.

The World Court and most foreign governments view settlements Israel has built in the areas as illegal. (Additional reporting by Tom Perry in Ramallah; Writing by Ori Lewis; Editing by Peter Graff)