Hamas has arrested three fighters who fired cross-border rockets into southern Israel from the Gaza Strip  on Thursday.

It is the first such detentions since the Islamists and Israel agreed a truce last month, fighters said.

An official with the Al Aqsa Martyrs Brigades, a militant faction of Palestinian President Mahmoud Abbas's Fatah movement, said Hamas security forces arrested three of its members who were involved in firing two rockets at Israel.

"They chased them after they fired the rockets and abducted them," the official said.

Hamas had no immediate comment.

Al Aqsa said it fired the two rockets into southern Israel after Israel's killing of an unarmed infiltrator from the coastal area earlier in the day, and Israel's killing of one of its members.

The rockets landed in an open area in southern Israel and no one was hurt, police spokesman Micky Rosenfeld said.

An Israeli army spokesman said soldiers shot dead a Palestinian who crossed into Israel from Gaza and ignored their calls to stop. Only later, Israeli forces saw that he had not been carrying a weapon, the spokesman said.

It was the first fatality along the Israel-Gaza frontier since the Egyptian-brokered truce went into effect. A Hamas spokesman said the killing was "a serious challenge" to the ceasefire.

The truce deal calls on Hamas to prevent cross-border rocket fire and attacks from the Gaza Strip and on Israel to halt its raids and ease an economic blockade.

Israel tightened restrictions on the passage of people and goods to and from the impoverished territory after Hamas seized control of it a year ago. United Nations officials said Gaza's goods crossings were still shut rather often despite the truce.

"There is not enough fuel, not enough food, there is not enough of anything," John Ging, an official with the UN Relief and Works Agency (UNRWA) that aids refugees, said in Gaza.

Although Israel has responded to cross-border rocket attacks by frequently shutting Gaza's crossings, records compiled by Western officials show up to a 44 per cent increase in goods imports in recent weeks, including a 30 per cent rise in fuel.

In the West Bank city of Nablus, Israeli troops raided several charity organisations and a medical clinic and closed down a local television station, Palestinian officials said.

Over the past several days, Israel has raided 15 Nablus charities over their suspected ties with Hamas.

Senior Hamas leader Esmail Haniya accused Palestinian National Authority officials of backing the Israeli operations.

But Palestinian Interior Minister Abdul Razzak Yahya condemned the raids and said the Palestinian National Authority would continue dealing with institutions that Israel ordered closed.

Meanwhile, a Palestinian journalist says Israeli border officials forced him to strip naked at gunpoint, a claim Israel denies.

Journalist Mohammad Omer says this happened June 26 at the Israeli-controlled Allenby Bridge between Jordan and the West Bank.

Journalist stripped

Omer was on his way home to Gaza after receiving a British journalism prize. He says Israeli agents insulted him, and he was forced to strip at gunpoint before collapsing amid the stress.

Israel says a thorough investigation shows his claims are "without foundation" and that he was not abused. A Palestinian doctor says Omer suffered a nervous breakdown but no injuries and was quickly released.

The Dutch government has asked Israel for clarifications.

Dutch diplomats later escorted Omer from the West Bank to Gaza, in line with Israeli requirements.

There is not enough fuel, not enough food, there is not enough of anything."