An Israeli demolition squad has smashed the foundations of a mosque being built near the Basilica of the Annunciation in Nazareth - the largest Christian church in the Middle East.
Some Muslim protestors were arrested after scuffles
An Israeli court ordered the demolition of the Shihab al-Din mosque - which did not have a building permit - in March.
Israeli security forces moved in with bulldozers at the site around dawn while most of the city's Muslims were sleeping.
Protestors headed to the site and several were arrested, and a number scuffled with the police, the BBC's James Reynolds says.
The mosque has been a source of contention for years between Muslim and Christian leaders and Israeli authorities.
Christian leaders said building a mosque so close to the basilica would be disrespectful.
Muslims cherish the site because a Muslim religious leader is buried there.
Pope John Paul II threatened to cancel a visit in 2000 over the issue, and US President George W Bush raised the subject
with Israeli Prime Minister Ariel Sharon during a meeting the following year.
About 40% of the Arab Israeli city of Nazareth is Christian, the rest of the population is Muslim.
But the Christian population has been shrinking, and is now estimated to be less than 4% of the population of Israel and the Palestinian-controlled areas.