Haifa (Israel) (AFP) - Foreign firefighting planes on Friday helped Israel tackle a wave of wildfires that have forced tens of thousands to flee their homes, as police announced a dozen related arrests.

Faced for the past four days with blazes across the country fed by drought and high winds, Israel received airborne assistance from Russia, Turkey, Greece and Croatia.

The flames in many places appeared to be easing somewhat despite the persistent wind, but a new fire erupted close to Jerusalem on Friday afternoon that the emergency services said was apparently started deliberately.

"Things can change and develop as we speak," police spokesman Micky Rosenfeld told AFP.

Support from France, Spain and others was due while a US Supertanker, considered the largest firefighting aircraft in the world, was expected to arrive Friday night.

Prime Minister Benjamin Netanyahu said Israel had also accepted pledges of support from Arab neighbours Jordan and Egypt, though the two governments declined to comment.

On the ground, Palestinian firefighters on Thursday night joined the Israelis, sending four fire engines to the northern city of Haifa and four more to the village of Beit Meir, near Jerusalem.

In nearby Nataf along the border with the occupied West Bank, a new fire broke out on Friday afternoon, with 20 planes and more than a dozen firecrews including four Palestinians trying to calm the blaze.

Fire department spokesman Kayed Daher said they believed the fire was caused by a Molotov cocktail thrown from a neighbouring Palestinian town.

In the country's third city Haifa, where tens of thousands had been evacuated Thursday from the path of towering flames which threatened entire neighbourhoods, residents started to assess the damage after police gave them permission to return.

The fires in the mixed Arab and Jewish city were "under control" on Friday, Rosenfeld said, but Daher said dozens of houses were completely destroyed.

The air was still thick with smoke, an AFP correspondent in Haifa said Friday, with the scale of the damage likely to become clear in the coming days.

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- Arrests, accusations -

Israeli foreign ministry spokesman Emmanuel Nahshon said some of the foreign planes were in action on Friday.

"We are deeply grateful to the international community," he said. "Its mobilisation proves that in times of crisis we can count on many friends in this region and beyond."

The rising number of fires since Tuesday has stretched Israel's capacity to deal with them, raising questions over lessons learned since a devastating blaze near Haifa killed 44 people in 2010.

The blazes, with dozens of outbreaks a day reported up and down the country Thursday, has fuelled Jewish Israelis' suspicions of the state's Arab minority and the Palestinians.

Arab Israelis make up about 17.5 percent of the country's population.

Descendants of Palestinians who remained on their land after the creation of the state of Israel in 1948, they largely identify themselves as Palestinians.

Statements by several Israeli officials have implicated Arabs, with Internal Security Minister Gilad Erdan saying that up to half of the blazes had been "arson terror".

Rosenfeld said they had made 12 arrests in the past 24 hours, without providing details on their identities.

Some are suspected of criminal negligence leading to accidental fires in tinder-dry woodland and undergrowth, while there are also suspicions that some may have been deliberate and related to the Israel-Palestinian conflict.

The Israeli army posted an aerial video of two men in a wooded area, saying the airforce had helped police in "apprehending suspects."

Prime Minister Benjamin Netanyahu said Friday there was "no doubt" some of the fires had been deliberate.

"There is a price to pay for the crimes committed, there is a price to pay for arson terrorism," he said during a tour of an airbase.

- 'Fire intifada'? -

Education Minister Naftali Bennett of the far-right Jewish Home party appeared to blame the alleged arson on members of the Arab minority when he said the fires could not have been lit by Jews.

"‎Only those to whom the land does not belong to are capable of burning it," he wrote on Twitter.

Some Israeli media joined in, speculating on the possible emergence of a "fire intifada", or Palestinian uprising, but the Yediot Aharonot newspaper disapproved.

"‎When the prime minister calls this terror, even if he doesn't say Arabs, a link is made that is supposed to be understood by everyone, '‎This is a wave of terror, the Arabs are burning down the country,'" its commentator Alex Fishman wrote.

"But it is a long road from that to calling this wave of fires in the last three days a 'fire Intifada'." ‎