Turkish police have fired tear gas on students protesting the start of controversial works on a road through their university campus in Ankara.

The tear gas was fired late on Friday as security forces shielded workers and diggers who began uprooting trees in a park on the site of Middle East Technical University (METU) in the Turkish capital on Friday night.

Dozens of students massed behind the gates of the establishment, angry with the planned destruction of 3,000 trees, Turkey's Dogan press agency reported.

The rector of the university, Ahmet Acar, strongly condemned the police action as illegal and said the university would take the matter to court.

"METU gave its green light to the road project but we do not approve of this night-time raid,", Acar was quoted as saying Saturday on the daily news website Hurriyet.

Greenpeace also issued a statement criticising the "antidemocratic and unacceptable" actions of the Ankara authorities.

The ongoing battle against the project has raged for weeks, with police using rubber bullets and tear gas in protests that drew in hundreds of students in early September.

METU's campus is one of the largest green spaces in the Turkish capital.

The latest protests come as Turkish authorities stand accused of committing "gross human rights violations" during anti-government protests that rocked the country in June and which began as demonstrations against the uprooting of green space in central Istanbul.

Amnesty International said in a report released on October 2 that "a string of human rights violations on a huge scale" were perpetrated by police.

What started as a relatively small environmentalist movement to save Istanbul's central Gezi Park from re-development evolved into a nationwide wave of protests against Prime Minister Recep Tayyip Erdogan, who is seen as increasingly authoritarian.

At least six people were killed and more than 8,000 people injured following the three weeks of demonstrations across the country in June, presenting Erdogan's Justice and Development Party (AKP) with its biggest challenge since it came to power in 2002.