The entrance, which had been sealed up for centuries, was opened by the Waqf, the organisation responsible for Muslim holy sites, on Monday.

The Waqf said the opening in the wall had been enlarged to provide light and air for basement rooms under the mosque.

But an Israeli spokesman said the new opening violated the agreement that neither side should introduce changes to the holy site.

Police officers were sent to the site in the early hours of Tuesday to seal the entrance up again.

A Palestinian labourer works near the outer wall opening of the Al-Aqsa compound

The Israeli Prime Minister, Ehud Barak, described the opening as "illegal and unilateral".

"We could not allow it to pass. I was glad that the police acted correctly," Mr Barak said.

Large numbers of Israeli police and border guards were sent to the site amid fears the move could trigger angry reactions from Palestinians.

Al-Aqsa is built on the remains of the second Jewish Temple, destroyed almost 2,000 years ago, making it a potential flashpoint for religious and national tension.

Renovating the mosque

But the mufti of Jerusalem, Sheikh Ikrima Sabri, accused Israel of looking for an excuse to intervene in the affairs of the holy shrine.

"There was a stone in the window, which the architect wanted to removed for light and air... Are we supposed to ask permission to repair every stone or to plant every tree," he said.

Renovations under the mosque have been taking place for some time.

Israeli archaeologists believe the opening is in fact part of the Jewish Temple's southern entrance built in the reign of Herod the Great.

They are concerned that remains of the Temple may be damaged while renovation work is carried out on the mosque.

The site has been at the centre of tension between Palestinians and Israelis a number of times in the recent past.

In September 1996, the Israeli government opened a controversial entrance to the Old City, sparking gun battles which left 80 people dead.

And in 1998, a Jewish extremist was convicted of attempting to attack the mosque by throwing a pig's head into its compound. Muslims regard pigs as unclean.