Eleven Palestinians, including a 16-year-old, were killed and more than 80 wounded by gunfire on Wednesday, the Palestinian health ministry said, when Israeli troops raided the flashpoint West Bank city of Nablus, drawing international appeals for calm.

The Israeli army said it was targeting suspected militants. Top Palestinian official Hussein Al Sheikh described the raid as a "massacre" and called for "international protection for our people".

Before dawn on Thursday Palestinian militants hit back, firing six rockets from Gaza into Israel.

The Israeli army said it intercepted five of them and that the sixth struck an uninhabited area.

Palestinian militant group Islamic Jihad claimed responsibility for the rockets after it called on "resistance forces" to respond to the "major crime" in Nablus.

The group said one of its commanders was killed in the West Bank raid.

Two hours later, the Israeli military launched air strikes on multiple targets in Gaza, sending plumes of black smoke into the sky.

The missiles targeted "a weapons factory" and a "military camp", both run by Gaza's Islamist rulers Hamas, the army said in a statement.

United Nations chief Antonio Guterres said the "immediate priority must be to prevent further escalation".

"The situation in the occupied Palestinian territory is at its most combustible in years," he said.

- Hospital 'covered in blood' -

The Israeli army said Wednesday's raid had targeted a "hideout apartment" used by suspects implicated in shootings in the West Bank.

It said one of the wanted suspects was "neutralised", along with two other people who opened fire on troops.

Both sides "exchanged fire" and rockets were also fired on the house by the army, spokesman Richard Hecht said.

Rocks, explosive devices and Molotov cocktails were hurled at the troops, said the army, which added that it suffered no casualties.

The Palestinian health ministry said those killed in Nablus were aged between 16 and 72.

Hours after the raid, the ministry announced the death of Anan Ennab, 66, from tear gas inhalation.

He had been in the market when the Israeli incursion began, his brother Allam Ennab said Thursday.

"What happened yesterday in Nablus was a real massacre, like I've never seen before," the 68-year-old told AFP.

Palestinian health officials said 82 people were treated for gunshot wounds. The Palestinian Red Crescent Society said its medics also treated 250 cases of tear gas inhalation.

The wounded include Palestine TV journalist Mohammed Al Khatib, who was shot in the hand, a colleague told AFP.

Talaat Ziada, the head of the intensive care unit in Nablus's Rafidia hsopital, said his youngest patient was an 11-year-old boy shot in the stomach and leg.

"It was a war zone in the Old City, and it was also a war zone here," he told AFP.

"The corridors and stairs were covered in blood, and people were scrambling to check on their relatives."

Wednesday's death toll was the highest since the second Palestinian intifada, or uprising, ended in 2005.

Palestinian shops were closed on Thursday in annexed east Jerusalem and elsewhere in the occupied West Bank, including Nablus, after a general strike was called in protest at the violence.

- 'Extremely concerned' -

The Lions' Den, a Nablus-based militant group, said six of those killed were members of various Palestinian factions.

Hailing the army's "courage", Israeli Defence Minister Yoav Gallant tweeted that Israel's "long arm" would reach "any terrorist".

US State Department spokesman Ned Price said Washington was "extremely concerned by the levels of violence".

Since December, Israel has been ruled by a coalition government regarded as the most right-wing in Israel's history. Prime Minister Benjamin Netanyahu handed key West Bank powers to far-right ministers.

The Palestinian health ministry announced Thursday a 30-year-old man died from his wounds, after being shot earlier this month by Israeli forces in Jenin.

Since the start of this year, the Israeli-Palestinian conflict has claimed the lives of 61 Palestinian adults and children, including militants and civilians.

Nine Israeli civilians, including three children, a police officer and one Ukrainian civilian have been killed over the same period, according to an AFP tally based on official sources from both sides.

Israel has occupied the West Bank since the Six-Day War of 1967.

Last year was the deadliest year in the territory since the United Nations started tracking casualties in 2005.

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