Turkish riot police fired tear gas and halted a march by some 100 students Saturday protesting against the clearance of trees on an Ankara university campus to make way for a controversial road development.

According to the left-wing student group, Genc-Der, which organised the demonstration, 26 people were arrested as they tried to march to the campus of the Middle East Technical University from Ankara city center.

Turkey said Saturday it was open to new bids in its plan to acquire its first long-range anti-missile system, should its controversial negotiations with China come to nothing.

"It is not a finalized deal yet. If U.S. and European companies make us better offers, we will continue to talk with them," said Foreign Minister Ahmet Davutoglu, who was quoted by Turkish newspapers.

Serbia accused Recep Tayyip Erdogan on Friday of meddling in the country's affairs after the Turkish Prime Minister said that "Kosovo is Turkey" during a recent visit to the former Serbian province.

Kosovo broke away from Serbia in 2008 but Belgrade still refuses to recognize its independence.

Iraq and Turkey on Friday vowed, following a meeting between foreign ministers, to improve relations between the two countries which have been marred in recent years by a series of disputes.

"We agreed to take new steps in order to improve bilateral relations and to open new horizons," Iraqi Foreign Minister Hoshyar Zebari told a news conference in Ankara.

Fierce clashes erupted in Syria overnight between Kurdish fighters and jihadists near the Iraqi border, the Syrian Observatory for Human Rights said Thursday.

"The clashes began around midnight (21:00 GMT Wednesday) and lasted around 12 hours, with the Kurds advancing in the direction of Al-Yaarubia, an area controlled by the Islamic State of Iraq and the Levant (ISIL) and other jihadist groups," the Britain-based monitor said.

The United States is "seriously concerned" about NATO ally Turkey's controversial decision to select a Chinese company for its long-range air and missile defense system, the U.S. ambassador said on Thursday.

"We are very concerned about a prospective deal between Turkey and Chinese firm that is sanctioned (by the United States)," ambassador Francis Ricciardone told reporters.

Syria has freed 64 women prisoners this week, or half the number expected to be released under a weekend hostage deal, a human rights activist said Thursday.

Nine Lebanese pilgrim hostages held for 17 months by a rebel group in northern Syria were exchanged on Saturday for two Turkish pilots abducted in Lebanon in August.

Turkish prosecutors have charged 33 people suspected of involvement in a May bomb attack that left 52 dead in a small border town and that Ankara has blamed on the Syrian secret service.

Prosecutors in the southern city of Adana are seeking life sentences for the suspects, two of whom are Syrian, after charging them with "murder with the use of explosive device", the Dogan news agency reported on Wednesday.

Turkish fighter jets intercepted a Russian military plane in international airspace over the Black Sea, the military said Wednesday, without giving a reason.

"Two F-16 jets were scrambled to prevent a potential violation of (Turkish airspace)" after the Ilyushin II-20 plane was detected flying in parallel to Turkish coast, the general staff said in a statement about Tuesday's incident.

Syrian authorities have released 16 women detainees as part of a weekend hostage exchange, but more than 100 others are still being held, a prominent human rights activist said Wednesday.

Nine Lebanese hostages held for 17 months by a rebel group in northern Syria were exchanged on Saturday for two Turkish pilots abducted in Beirut in August.