U.N. aid workers stepped up calls Thursday for an urgent Gaza ceasefire, warning that spiralling violence endangered their ability to respond to the needs of the 1.8 million affected population.

The Lebanese army has arrested an Arab-Israeli civilian who cut through barbed wire to cross the border into Lebanon, a security official said on Thursday.

"Ibrahim Zaydat entered Lebanon on Wednesday afternoon after cutting through a small section of barbed wire at the southeastern border, and was arrested by the army," the official told Agence France Presse.

The armed wing of Hamas has executed three Palestinians and arrested seven others for allegedly collaborating with Israel during the Gaza war, a website close to the movement reported Thursday.

The Majd website quoted a senior security official in the enclave as saying seven people had been arrested on suspicion of scoping out targets for Israel and that three others had been shot dead.

Venezuelan President Nicolas Maduro made a surprise visit to Cuba to meet with Fidel Castro, who praised his guest's "solidarity" with the Palestinian people and condemned the "genocide" in Gaza.

The former Cuban president and leader of the island's communist revolution said Maduro had made the visit Tuesday during a "foreign trip regarding the defense of his country's major oil interests."

Palestinian President Mahmud Abbas held talks with exiled Hamas leader Khaled Meshaal on Thursday as renewed fighting raged in Gaza following the collapse of Egyptian-brokered truce efforts.

The talks in Doha, where Meshaal is based, were hosted by Qatari Emir Sheikh Tamim bin Hamad al-Thani, a key backer of the Islamist movement which dominates Gaza, the Gulf state's QNA news agency reported.

An Israeli infantry unit combed on Thursday the heights near the tiny village of Wazzani and the occupied town of Ghajar in southern Lebanon, the state-run National News Agency reported.

NNA said that the unit was backed by a Humvee and an Israeli drone that overflew al-Abbasiyeh and the occupied Shebaa Farms area.

Israeli warplanes killed three top Hamas commanders in southern Gaza on Thursday, inflicting a heavy blow on the movement's armed wing after failing to kill its top military chief.

As the six-week war between Israel and Hamas raged on, leaving Egyptian mediated truce talks in tatters, warplanes pounded Gaza killing three members of the Islamist movement's armed wing, the Ezzedine al-Qassam Brigades.

The United States on Wednesday charged Israel had targeted members of a Palestinian family whose teenaged son was kidnapped and killed in July along with two cousins, who are U.S. citizens.

Tensions between Palestinians and Israelis in annexed east Jerusalem plunged to a new low on July 2 when 16-year-old Mohammed Abu Khder was snatched from an east Jerusalem street and later found burned alive.

Thirty-one Palestinians have been killed and at least 120 wounded by Israeli strikes across Gaza since the collapse of a temporary truce, the emergency services said Wednesday.

And the armed wing of Hamas warned foreign airlines against flying into Tel Aviv, threatening to step up its six-week conflict with Israel and declaring truce talks in Cairo over.

A Cairo court on Wednesday sentenced an Israeli tried in absentia to life imprisonment and a Jordanian telecoms engineer to 10 years in jail for espionage on behalf of Israel.

Bashar Ibrahim Abu Zeid from Jordan was arrested in April 2011 and accused of trying to recruit Egyptian engineers to help Israel intercept telephone calls in Egypt.