Hamas officials said the incidents were not robberies and that police were there to ensure the bank handed over money that customers rightfully sought to access.

But officials at the Palestine Monetary Authority in the West Bank city of Ramallah said armed men forced their way into a branch of the Palestine Investment Bank in Gaza City on Tuesday and again on Wednesday.

"Yesterday (Wednesday) and the day before, a group of armed men wearing military clothing and protected by police stormed the investment bank and took a total of $350,000 from the bank's reserves," said Mohamed Manasira, deputy director of the oversight department at the authority.

Manasira said $100,000 was taken from the bank on Tuesday and $250,000 on Wednesday.

The Hamas-run interior ministry confirmed the incident, but denied it was a robbery. It said police were merely protecting the interests of bank customers who had been unable to withdraw funds.

It said Gaza businessmen had approached the police after the bank said it could not cash their cheques because it had insufficient cash funds and then, a day later, told them it had been ordered by its Ramallah office to transfer the money to the West Bank.

The Palestine Investment Bank reportedly told the customers that the money transfer had been ordered by the Ramallah-based Palestine Investment Fund, an investment institution set up and administered by the Palestinian Authority.

"In order to protect the Palestinian people's money ... the police went to oblige the bank's administration to pay the amounts and not -- as certain suspicious websites have said -- to carry out an armed robbery," the statement said.

Hamas and the Fatah-dominated Palestinian Authority have been fiercely divided since the Islamist group seized power in Gaza in June 2007 following months of unrest after it won elections a year earlier.

The two rival governments operate separate ministries and courts, and each considers the other to be illegitimate.

The Ramallah-based Monetary Authority condemned the "seizure by force of arms of amounts of cash under the pretext of cashing cheques ... in a way that is against all laws and norms of banking."

It announced "the suspension of banking in all branches of banks operating in the Gaza Strip on Thursday ... as an expression of resentment, denunciation and condemnation for these deplorable attacks."

The closure is the second time that banks in the Hamas-run Gaza Strip have shut down to protest the seizure of funds by gunmen allegedly linked to the Islamist group.

In June, banks closed after Hamas police reportedly seized $16,000 in a raid carried out following a Hamas court order to release funds that had been frozen by the Western-backed Palestinian Authority.

The monetary authority, the Palestinian central bank, refuses to have any dealings with the Islamist Hamas movement, in part because it is blacklisted as a terrorist group by Israel, the United States and the European Union.

The National Islamic Bank, Gaza's sole financial institution affiliated with Hamas rather than the monetary authority, remained open on Thursday, and did not close during last year's strike.