CAIRO (Reuters) - Egyptian police on Sunday raided the press syndicate in Cairo and arrested two journalists critical of the government, a syndicate official and reporters said in what the syndicate called an unprecedented crackdown.

The interior ministry denied officers had stormed the press labour union building, a traditional spot in downtown Cairo to stage protests, but confirmed some of its members had arrested the journalists inside the syndicate.

Security forces have sought to quell dissent since thousands took to the streets on April 15 to protest a decision by President Abdel Fattah Sisi to hand over two islands to Saudi Arabia. Police dispersed smaller protests two weeks later.

On Sunday, journalists held a sit-in inside the union when officers arrested two of them working for the opposition website Bawabet Yanayer including its editor, syndicate officials said.

"The incident is true and at the very least the interior minister has to be fired and there needs to be an apology," Khalid al-Balshy, a syndicate board member told Reuters.

Mahmoud Kamel, a member of the syndicate board, said over 40 policemen raided the building but the interior ministry said its force consisted of only eight officers.

"The ministry affirms that it did not raid the syndicate or use any kind of force in arresting the two journalists who handed themselves in as soon as they were told there was an arrest warrant," the interior ministry said in a statement.

A security guard was wounded in the eye when police raided the union, Kamel said.

"There was an arrest warrant for the two journalists issued a week ago but the syndicate was negotiating with the interior ministry over the matter," he said.

The syndicate council called for an indefinite strike among Egyptian journalists until the interior minister resigns and urged newspapers to black out their front pages.

"This is unprecedented, no president or prime minister or interior minister has ever dared to do something like this," Kamel said. Under the law only a prosecutor is allowed to search the union in the presence of its chairman or deputy, he added.

Dozens of journalists later held a new sit-in at the syndicate to protest against the arrest, a reporter said.

Sisi faces criticism for putting the uninhabited Red Sea islands of Tiran and Sanafir in Saudi waters and a faltering economy though there are no signs that his rule is under threat.

(Reporting by Cairo newsroom; Editing by Andrew Hay)