A court in Istanbul began a retrial on Tuesday over the murder of an ethnic Armenian journalist, a case that has gripped the nation for years and sparked accusations of state conspiracy.

Hrant Dink, who incurred the wrath of Turkish nationalists for calling the World War I massacre of Armenians a genocide, was shot dead in broad daylight in 2007 outside the offices of his bilingual weekly newspaper Agos.

The man accused of instigating the 2007 murder of ethnic Armenian journalist Hrant Dink in Turkey, along with 18 other suspects, will go back to court on Tuesday after an earlier verdict was overturned.

A hearing on the retrial will take place at a high criminal court in Istanbul where a large crowd is expected to gather to pay tribute and demand justice for Dink, who was a leading member of Turkey's tiny Armenian community, Garo Paylan of the Association of Friends of Hrant Dink told Agence France Presse.

Turkey said it had downed a Syrian military helicopter on Monday, accusing the neighboring nation of violating its airspace in the tense border region, amid a new international diplomatic push to end Syria's civil war.

The Syrian MI-17 helicopter was detected two kilometers (1.2 miles) inside Turkish airspace and shot down five minutes later after failing to heed warnings, Deputy Prime Minister Bulent Arinc told reporters after a weekly cabinet meeting.

Riot police used tear gas and water cannon to disperse anti-government protesters in several Turkish cities overnight Monday, as demonstrations against the Islamic-rooted cabinet simmered across the country, media reported.

In Istanbul's Kadikoy district, which has become the focal point of the demonstrations, hundreds of protesters set up barricades, which they then set on fire, according to NTV television.

Turkey on Sunday welcomed a U.S.-Russian deal aimed at disarming Syria of its chemical weapons but warned that Damascus could be seeking to buy more time for its deadly military campaign.

"As a matter of principle, Turkey welcomes the disposal of weapons of mass destruction anywhere in the world, and particularly of chemical weapons in our region," a government statement said.

Turkish police said Saturday that an autopsy will be performed on the body of a man whose death the previous day the opposition has blamed on police use of tear gas.

Serdar Kadakal died on Friday in the Kadikoy district of Istanbul, an area that this week become the center of anti-government protests and where riot police have been using tear gas for three consecutive nights to disperse demonstrators.

Turkish police used water cannon and tear gas late Thursday to break up fresh anti-government protests in Istanbul, amid anger over the death of a demonstrator earlier in the week.

Officers faced 2,000-3,000 angry protesters on a second consecutive day of demonstrations in the Kadikoy district, an opposition stronghold.

Turkish Prime Minister Recep Tayyip Erdogan on Thursday cast doubt on a proposal to secure Syria's chemical weapons, saying the Syrian government should not be trusted and is only seeking to stave off an international intervention.

Erdogan said that Damascus has "violated all of its promises in order to buy more time to continue massacring people, and it will continue to do so."

Police used water canon and tear gas overnight Wednesday in a bid to break up fresh anti-government protests across Turkey, media said.

Thousands of people angry over the death of a 22-year-old demonstrator in southern Turkey on Monday clashed with police in Istanbul, the capital Ankara, the western city of Izmir as well as in the southern cities of Mersin and Atakya.

Turkey's Interior Minister Muammer Guler said Wednesday that protesters were attempting to use the death of a young man during a demonstration to "spread chaos" as pockets of anti-government unrest flared once again in the country.

As tensions rose, the country's Kurdish rebels for the first time called on their supporters to join demos against Prime Minister Recep Tayyip Erdogan, seen by critics as increasingly authoritarian.