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sole power plant will have to shut down within 48 hours if a strengthening of the blockade imposed on the Strip by is not ended, officials warned on Thursday, as border tensions simmered following the arrest of a Palestinian militant leader.

Israeli authorities have closed all crossings into , cutting off access for the fuel trucks that supply the plant, over fears of retaliation attacks following Monday's arrest of Bassam Al-Saadi, a senior leader of the Palestinian Islamic Jihad group.

The restrictions are an intensification of a siege that has been in place since 2007.

The blockade has a serious impact on living standards for residents of impoverished Gaza, and rights groups have slammed it as a form of illegal collective punishment.

Already facing cuts that leave them with just 10 hours of electricity a day, Gaza residents would face further blackouts if the plant stopped operating, leaving the enclave's only external source of power a daily feed of 120 megawatts that comes from Israel.

"That would have a grave impact on the daily life of over two million people and vital services," said Mohammad Thabit, of Gaza's power distribution company.

As well as stopping the transport of goods and aid into Gaza, the shutdown - which entered its third day on Thursday - has also prevented workers from crossing into Israel.

Residents on the Israeli side have complained of restrictions on movement.

Egyptian mediators stepped up efforts with Israel and Palestinian Islamic Jihad to lower tensions after Saadi's arrest during a raid in the occupied West Bank city of Jenin, in which a 17-year-old member of Islamic Jihad was killed.

The group declared full alert among its fighters, implying a threat of imminent retaliation, after footage circulating in Israeli media appeared to show Saadi may have been hurt during his arrest.

Israeli authorities have closed all crossings into the besieged Gaza Strip until further notice amid concerns of retaliatory attacks by the Palestinian Islamic Jihad, following the arrest of its West Bank-based leader Bassam al-Saadi ⬇

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"We are in contact with Egyptian officials but so far there is no satisfactory result, therefore, the full alert status remains," said Daoud Shehab, an Islamic Jihad spokesman.

Abdel-Latif Al-Qanoua, a spokesman for Hamas, the militant group that rules Gaza, condemned Israel's closures and said his group had also been in talks with mediators.

"We will not accept the continued closure of crossings and the policy of collective punishment," he said.

Israeli officials have so far offered no comment on the circumstances of arrest and suggested the tightened blockade will remain in place while the Islamic Jihad threat persists.

(Reuters, °®Âþµº)