A Palestinian was killed and at least four others wounded in an Israeli airstrike on a tunnel on Gaza- Egypt borders, medical sources and witnesses said on Friday.

The attack was the latest in a series of bombings the Israeli airplanes has carried out in the Gaza Strip early Friday.

Smugglers were working in the tunnel when the incident happened. A number of workers are still trapped in the underground tunnel.

Medical sources said the dead was a teenager, whose head was separated from his body.

Four earlier Israeli airstrikes took place, targeting open spaces and a training site for the Islamic Hamas movement, security sources and witnesses said.

The Israeli army started the attacks around midnight, and said that the targeted places were used by Palestinian militants to produce, store and fire rockets into Israel.

An Israeli army spokesman told Xinhua that the first airstrike hit a building "used to fire rockets from." The three other raids hit open lands in Central and Southern Gaza Strip.

The spokesman, Avichai Adraee, threatened that the Israeli army will continue its operations as long as Palestinian fighters launch missiles.

The Israeli raids took place hours after a rocket landed in port city Ashkelon in southern Israel. The rocket caused no injuries or damage.

On Thursday morning, Palestinian militants fired mortars at Israeli army posts near Gaza Strip's commercial crossings and Israel closed one crossing in response.

Ten mortar shells landed near Kerem Shalom crossing, which Israel uses to deliver limited amounts of humanitarian aid and fuel to the besieged territory, and a military site near the closed Kissufim passageway in southeast Gaza Strip.

Following the incident, Radio Israel said that Kerem Shalom crossing was sealed off.

Also on Thursday, Israeli planes dropped flyers in northern Gaza Strip, warning residents to stay away from an electric fence between the Hamas-controlled coastal Strip and Israel.

The leaflets, with telephone numbers and email addresses on them, urged people to inform the army of any activities of the Palestinian militants in the border area.