A group of supporters of Turkish Prime Minister Recep Tayyip Erdogan on Sunday attacked anti-government demonstrators who were fleeing the police during clashes with security forces in downtown Istanbul, the daily Hürriyet reported.

According to the newspaper, a group of some 30 or 40 men armed with sticks sallied forth from the Kasimpasa neighborhood, a stronghold of the government Justice and Development Party, and headed for Istiklal Street, where they attacked anti-government demonstrators who were fleeing from a police tear gas onslaught.

The armed men pursued the demonstrators to the local headquarters of the opposition Republican People's Party, or CHP, where they destroyed the offices' glass doors.

Many reports on the social media said Sunday that after the pro-government rally staged by Erdogan in Istanbul, groups of government supporters emerged from neighborhoods near Taksim Square, the epicenter of the protests, to chase and beat anyone they could catch who appeared to be involved in the anti-government protests.

In photos and videos, groups of young men armed with sticks can be seen walking alongside police vehicles.

This is the first time that pro-government supporters have participated violently in the protests that erupted almost three weeks ago, resulting in clashes between police and demonstrators in many cities around the country, including the capital of Ankara.

Protesters ranged through Istanbul's streets all Saturday night clashing with security forces and dawn brought no immediate letup to the confrontations, although they had temporarily abated somewhat by noon on Sunday.

However, along Istiklal St. police began firing rubber bullets and smoke bombs around 1300 GMT to try and prevent a group of protesters from advancing to Taksim Square, which had been cordoned off by police.

Elsewhere, security forces used water cannon and pepper spray against demonstrators protesting what they say are government excesses.

The protests were sparked almost three weeks ago when thousands of people occupied Istanbul's Gezi Park to prevent its destruction by city authorities, but they have since spread to dozens of cities around Turkey.

Erdogan on Sunday once again denied that there is any supposed environmental aspect to the protests, saying that the aim of the demonstrators is to harm Turkey.

Two of the largest Turkish unions and three professional colleges on Sunday announced a general strike for Monday, as well as street protests in the country's major cities.

Only accredited journalists were being allowed free passage through the zone by security forces on Sunday, and the circulation of tourists was severely restricted by authorities.

In an effort to prevent protesters from congregating in Taksim Square, the government on Sunday invoked the anti-terrorism law, with European Affairs Minister Egemen Bagis saying in a television interview that "From this moment on, any person found there regrettably will have to be considered ... as a member of a terrorist organization."

According to NTV television, about 40 people were arrested on Sunday in Istanbul during different clashes around Taksim Square. EFE