The sound of gunfire was heard across Jenin as wounded Palestinians continued to arrived by ambulance to the northern West Bank city's Ibn Sina hospital into the early afternoon, an AFP journalist said.

The Palestinian health ministry said four people had been killed and at least 62 others were wounded in the violence.

One of those killed was a teenager, 15-year-old Ahmed Saqer, the ministry said in a statement.

It named two of the other fatalities Khaled Assassa, 21, and Qassam Abu Saria, 29.

In a statement, Palestinian Islamic Jihad claimed Abu Saria as a fighter for the militant group.

Jenin's deputy governor, Kamal Abu al-Rub, told AFP the Israeli forces had launched the raid at around 4:00 am (0100 GMT).

"The army stormed the (Jenin refugee) camp and the city after the dawn prayer in large numbers, and there was intense gunfire," he said.

An AFP journalist confirmed fighting was still ongoing as of 2:25 pm (1125 GMT).

- 'Deteriorating situation' -

The Israeli army said an armoured vehicle had been hit by a "very unusual and dramatic" explosive device at around 7:10 am (0410 GMT), during "routine activity" to arrest two "wanted suspects" -- one affiliated with Islamist movement Hamas and the other with Palestinian Islamic Jihad.

"We had five Israeli border police guys wounded, and two soldiers also lightly wounded," army spokesman Richard Hecht said. "From that point, we had to extract our injured."

"It will take a few hours, it's going to be pretty harsh, there is a lot of fire," he added in the early afternoon.

The army said that an Apache helicopter had fired missiles in support of the soldiers, a rare measure in the West Bank.

An AFP photographer in Jenin witnessed a helicopter fire two missiles as well as a Palestinian journalist who had been injured in the fighting.

A Palestinian intelligence official told AFP on condition of anonymity it was the first time since 2002 -- during the second Palestinian intifada, or uprising -- that the Israeli army has fired missiles from an aircraft during a raid in Jenin.

The United Nations rights chief, Volker Turk, said he was "extremely worried by the deteriorating situation".

"Unlawful killings of Palestinians by the Israeli security forces have increased, including apparent extrajudicial executions," he added.

Violence in the Israeli-Palestinian conflict has escalated over the past year, coinciding with the hard-right government of Prime Minister Benjamin Netanyahu took power in December.

- 'Open war' -

The Palestinian health minister, Mai al-Kaila, called in a statement for the "urgent" dispatch of blood and medical supplies to Jenin.

Hussein al-Sheikh, the Palestinian Authority's civil affairs minister, said a "fierce and open war is being waged against the Palestinian people... by the occupation (Israeli) forces".

He called for the Palestinian leadership to take "unprecedented decisions" without elaborating.

Speaking as the raid unfolded, Israeli Defence Minister Yoav Gallant said: "We will use all the tools at our disposal and strike terrorists wherever they may be."

Israel has occupied the West Bank since the 1967 Six-Day War and its forces regularly launch incursions into Palestinian cities, which are nominally under the control of president Mahmud Abbas's Palestinian Authority.

Jenin and its adjacent refugee camp -- which was besieged by the army in 2002 and saw deadly fighting -- have frequently been the site of violent clashes between Israel and the Palestinians.

In March, four Palestinians were killed during the a raid on the camp.

Ten Palestinians were killed in another operation in the camp in January -- at the time the deadliest single raid in the West Bank for 20 years. An incursion into Nablus the following month killed 11 Palestinians.

Since the start of the year, at least 163 Palestinians, 21 Israelis, a Ukrainian and an Italian have been killed in violence linked to the Israeli-Palestinian conflict, according to an AFP tally compiled from official sources.

The figures include combatants as well as civilians and, on the Israeli side, three members of the Arab minority.