Unmanned aircraft is said to have been downed using Patriot missile near city of Ashdod on southern coast

Israel claims to have downed a drone from the skies above its southern coastline. The unmanned aircraft, which Israel says was launched from Gaza and shot down with a Patriot missile near the city of Ashdod, is the first weapon of its kind Israel has encountered in this conflict.

Rockets were also fired into Israel from Lebanon early on Monday morning, drawing retaliatory fire from Israeli forces. This is the third such rocket attack from Lebanon since Friday. There were no reported casualties.

In the West Bank, a 21-year-old Palestinian was killed in Hebron after clashes between the Israeli military and protesters against the war in Gaza – the first Palestinian casualty in the West Bank since the conflict began.

The dead man – identified in unconfirmed reports as Muneer al-Bardeen – was shot during a protest at al-Samoua junction, 20 minutes south of Hebron.

Witnesses said Bardeen was shot with live ammunition at around 3am, after hours of clashes that began after Iftar, the breaking of the Ramadan fast, and carried on throughout the night.

On Monday morning, Palestinian media reported that two other men were injured in the clashes – Mahmoud Yasser Muhammad Breghith, 21, who was shot in the leg, and Mahmoud Nasser Juma Hitawi, 20, shot in the foot.

Hebron is one of the cities most heavily affected by Israel's incursions into the West Bank following the kidnapping of three Israeli teenagers in June. The two main suspects in the murder of the three boys are Hamas members living in Hebron. They are still at large.

An Israeli Defence Force spokesman could not be reached for comment.

At least 172 Palestinians have been killed in the Gaza Strip since the Israeli offensive began seven days ago. The UN estimates that 77% of those killed have been civilians.

The Palestinian president, Mahmoud Abbas, was set to discuss moves to seek UN intervention at an emergency meeting of Arab foreign ministers in Cairo on Monday after another night of air strikes on Gaza in which Israeli war planes struck more than 40 sites, including three training facilities used by Hamas's armed wing, killing two people.

The UN chief, Ban Ki-moon, urged Israel to scrap plans for a ground offensive, saying "too many" Palestinian civilians had been killed.

Thousands of Palestinians fled their homes in two northern areas of the coastal enclave on Sunday after Israel warned it would "strike with might" against what it says are rocket-launching sites – an attack that has not yet materialised.

The exodus from Beit Lahia and Attatra came after Israel dropped leaflets and sent text messages warning civilians to evacuate northern Gaza by midday on Sunday in advance of a large-scale bombing campaign. The area is home to at least 100,000 people.

The UN says 17,000 people have sought refuge in its facilities.

A senior Israeli military officer, in a telephone briefing with foreign reporters, said Israel would strike the Beit Lahia area from late evening on Sunday. "The enemy has built rocket infrastructure in between the houses [in Beit Lahia]," the officer said. "He wants to trap me into an attack and into hurting civilians."

The leaflet warned: "Those who fail to comply with the instructions will endanger their lives and the lives of their families. Beware."

As the ultimatum drew near, large numbers raced by in pickup trucks or on donkey carts, waving white flags, with many heading to UN-run schools that were taking in refugees. "They are sending warning messages," said one resident, Mohammad Abu Halemah. "Once we received the message, we felt scared to stay in our homes. We want to leave."

Outside one UN school, there were rows of horses tied up by families anxious to protect their animals.

During a visit to Beit Lahia after the deadline had expired, the Guardian saw that most residents had opted to stay in their homes. Some shops were open and hospitals called for volunteers from medical schools to help treat an expected influx of casualties.

The warning was issued hours after Israeli naval commandos launched an early morning raid on a beach in the Sudaniya neighbourhood in the north of Gaza City, targeting another rocket-launching site. On Saturday, the coastal enclave suffered the bloodiest day of the six-day Israeli assault, with 54 Palestinians reported killed.

There has been speculation that Israel may launch a ground offensive into Gaza, a move likely to sharply increase the number of civilian casualties. At least 30 children were among those killed, according to Gaza's health ministry. There have been several Israeli injuries but no fatalities.

In the worst single incident of the conflict so far, at least 17 people were killed and 45 injured when two large Israeli bombs hit a house in the Tuffah neighbourhood of Gaza City where the city's chief of police, Tayseer al-Batsh, was sheltering. Five other people were missing, presumed dead.

Most of the injured were returning home from a mosque when they were caught by shrapnel from the blast.

Israel has been massing tanks and soldiers at Gaza's borders, which some fear could signal a wider ground offensive that would cause heavy casualties. "We don't know when the operation will end," the Israeli prime minister, Binyamin Netanyahu, told a cabinet meeting on Sunday. "It might take a long time."

The beach raid by several dozen commandos at 2am on Sunday was the first time Israeli forces have set foot in Gaza since the beginning of the current campaign. Four commandos were reportedly lightly injured after apparently being spotted approaching and being engaged by waiting Palestinian fighters.

Saad al-Dawla, the night watchman of the Mathaf hotel, said he was sleeping when the commandos came to the beach. "I was sleeping in the lobby with a friend. At the beginning we heard shooting from the Palestinian side. I got up and looked out the window and saw that there were people shooting from the water. Almost immediately an [Israeli] helicopter came and started shooting at the water as well," he said. "Later I heard shelling from the sea and the sounded of a warship's siren. The whole thing last about two hours."

Asked whether Hamas or other groups had watchers near the beach, Dawla said he did not know. Ladders at a mosque overlooking the beachfront and leading to its tower strongly suggested that a sentry had been posted there.

Israel has launched more than 1,300 air strikes since the offensive began, the military spokesman Lt Col Peter Lerner said. Palestinian militants have launched more than 800 rockets at Israel, according to the Israeli military.

Israel has said it is acting in self-defence against rockets that have disrupted life across much of the country. It also accuses Hamas of using Gaza's civilians as human shields.

Critics say Israel's heavy bombardment of one of the most densely populated territories in the world is the main factor putting civilians at risk.