Israeli forces have shot and killed three Palestinians by Gaza's perimeter fence, the Israeli military has said.

The Israeli army said the group threw an explosive device towards them after attempting to cross the fence from the besieged Gaza Strip on Tuesday evening.

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It said troops had cordoned off an area near the southern end of the Palestinian coastal enclave after spotting "three suspects" crossing the frontier.

"[They] searched the area towards the suspects who hurled a grenade or explosive device at the troops," who then opened fire on the three Palestinians, the military said in a statement.

A military spokeswoman confirmed they were killed.

Local media reported that the three slain Palestinians were identified as Mohammad Abu Mandeel, Salem Zuweid an-Na'ami, and Mahmoud Khaled Sa'id.

The three were from al-Maghazi in the central Gaza Strip.

A police source in Gaza told Reuters News Agency they were civilians without affiliations with armed groups in Gaza. He questioned the Israeli account that they threw explosives towards troops.

Hani Abu Mandeel, 46, father of Mohammed Abu Mandeel, told Al Jazeera that his son went missing along with his friends on Tuesday evening.

"Until this moment, we didn't receive any information from the Red Cross, civil affairs or any side uncovering the fate of our son and the other boys," he said.

"We call on all concerned bodies, Red Cross, Palestinian Authority and human rights groups to intervene. We want to know if our children are alive, injured or killed, and if so, we want their bodies."

"The three boys are friends, neighbours and classmates. They used to hang out every day in our farming land near the eastern border of Gaza. We live a one-kilometre away from the fence," he added

Commenting on the Israeli army statement that they were holding explosive devices, Hani said: "They are only children at the age of 17 and didn't have any military actions."

A spokesman for Hamas, the group which governs Gaza, said the Palestinians were killed "in cold blood".

"The killing of the three Palestinians last night is a heinous crime, and a form of an organised Israeli terrorism against our Palestinian people for decades," said Fawzi Barhoum in a statement.

Ceasefire efforts

The incident along Gaza's fence threatened to undermine efforts to reach an informal ceasefire between Israel and Hamas.

Earlier on Tuesday, a senior Hamas official said incendiary balloons Palestinians recently launched from the Gaza Strip were a signal to Israel to accelerate unofficial "understandings" meant to ease the crippling 12-year blockade on the enclave.

Israel has conducted three military assaults on Gaza since Hamas took control of the territory, with dozens of other smaller skirmishes taking place.

A two-day surge in violence in November between Israel and the armed Gaza-based faction, Islamic Jihad, left 34 Palestinians dead and dozens of Israelis injured.

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For the past 20 months, weekly demonstrations have been organised along the fence, demanding an end to the 12-year blockade.

More than 200 Palestinians, mostly unarmed, were killed by Israeli fire during the marches and hundreds of others were badly wounded.

Israel, which drew international accusations of using excessive force, has said it is defending itself from attacks and attempts to breach the fence.

Israel and Egypt keep the Gaza Strip under a blockade, tightly restricting movement out of the territory that is home to two million Palestinians.

Hovering at about 50 percent, Gaza's unemployment rate is one of the world's highest and most of the population relies on humanitarian assistance.