Prime Minister Benjamin Netanyahu said on Monday that Israel will close the Kerem Shalom border crossing with Gaza over the airborne firebombs being sent into Israel in recent weeks.

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"In agreement with the defense minister, we will act with a heavy hand against the Hamas regime in the Gaza Strip," Netanyahu said.

Hamas spokesman Fawzi Barhoum called the step "a new crime against humanity" that are against international law and human rights.

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This was not the only step Israel is taking to counter the threat, Netanyahu said, but refused to elaborate. "As for Gaza, I've already told you that I have no intention to prematurely announce all of the steps we are taking," the prime minister told Likud lawmakers. "There will be other steps which I won't detail."

In recent weeks Israeli fields and forests near the Gaza border have been set ablaze by incendiary kites and helium-filled balloons launched from the Strip. Some balloons carried small explosive devices in a new tactic.

Israel has accused Hamas of stoking violence in an attempt to deflect domestic opinion from Gaza's energy shortages and faltering economy.

Kerem Shalom is the only crossing for goods into the Gaza Strip. There are two other crossings whose use is limited. The Erez crossing is used for people only. The Rafah crossing, on the border with Egypt, opens from time to time to allow the passage of goods and construction materials.

The IDF spokesperson's office said in a statement that the crossing was being shut "in light of the continuation of arson terrorism and other terror attempts" lead by Hamas, and that the step had been recommended to Netanyahu by the IDF Chief of Staff Gadi Eisenkot.

The crossing would be shut to all good but humanitarian supplies such as food and medicine, the IDF said, adding that such supplies would be allowed into Gaza only on the basis of case-by-case approval by the government's coordinator for the terroritories.

"There shall be no import or export of any goods to and from the Gaza Strip," the statement said.

Gaza fishermen would also be limited to fishing just six nautical miles out to sea, rather than nine miles as had been permitted for the season until Monday, the IDF said.

Defense Minister Avigdor Lieberman said he had ordered stiffer measures taken at all the crossings.

"They are burning grasslands and fields on a daily basis," Lieberman said, adding that the entire land area that had been torched thus far by burning kites and other incendiary devices was roughly equal to the land areas of Israeli cities such as Netanya and Rehovoth.

"We do not intend to take this and continue on in this fashion. I suggest that they first of all straighten out and stop the provocations along the fence and the fires," Lieberman said.

"In the coming days we will make it more difficult at all the crossings. This cannot go on like this. I have ordered the IDF to take some steps and they shall see that this cannot o on unilaterally," he added.

Mohammed Abu Jiyab, an expert on the Gaza economy and editor of a magazine on the subject said the closure of Kerem Shalom "will lead to the collapse of an economy already in crisis, bankrupt many businesses in the strip, and cost a loss of jobs that will worsen unemployment and seriously hurt the service sector."

On Thursday some 750 acres (3,000 dunams) of brush in the Negev's Gerar Riverbed were set alight as a reslt of either a burning kite or balloon sent from Gaza. There were seven other fires in the Shaar Hanegev region. Fires also erupted in several spots in the Gaza border region as well, including at Beeri and Kissufim.