The Kerem Shalom crossing in southern Gaza, designated for the entry of essential supplies to the Palestinian territory, and the northern Eretz crossing, which allows the passage of people to and from the Gaza Strip, have both been closed for several days.
Israeli officials said the closures were in response to fears of a violent Palestinian reaction to a recent Israeli army operation in the West Bank city of Jenin, in which two senior Islamic Jihad militants were arrested.
Gaza's only power station is at risk of imminent shutdown due to a lack of fuel, its manager warned on Thursday as Israel's complete closure on the territory entered a third day.
The measures have halted deliveries through Israel of diesel, which is needed to fuel Gaza's sole power plant.
Israel has also imposed restrictions of the movement of Israelis living near Gaza, ordering them to stay close to underground shelters.
Thousands of Gazans with permits to work in Israel have also been unable to travel across the checkpoint.
During the Jenin raid last Monday, the Israeli army killed a 17-year-old Palestinian in a clash with locals.
The teenager, identified as Dirar al-Kafrayni, was prounounced dead by Palestinian medical sources, hours after he sustained serious injuries in the head.
Palestinian security sources named one of the arrested members of the Islamic Jihad group as Bassem al-Saadi, a leader of group's political wing.
The second man arrested was identified as Saadi's son-in-law, who is accused by Israel of organising fundraising campaigns for Islamic Jihad.
The deadly flashpoint city of Jenin
Since March, Israeli army has frequently raided the West Bank city of Jenin, following several stabbing and shooting attacks by Palestinian young men, including some from Jenin.
Over the same time period, Palestinian sources said 55 Palestinianw have been killed and dozens others injured and arrested.
Palestinian stabbing and shooting attacks, mainly inside Israeli towns and cities, have claimed the lives of 19 Israelis.
Conditions in Gaza worsen
In the Gaza Strip, the Islamic Jihad group has reportedly been involved in retaliatatory rocket fire into nesrby Israeli areas.
Responding to the closure of Gaza's border crossings, civil society organisations denounced the Israeli decision, which they say would further worsen economic conditions for Gaza's 2.3 million residents.
Since 2007, Israel has imposed a land and marine blockade on the Gaza Strip, causing economic hardship, with high unemployment and poverty rates.
According to UN statistics, more than 80 percent of the Gaza population relies on regular food aid, provided by the United Nations Relief and Works Agency.
