Turkish security forces have killed 25 Kurdish militants this week as they battle suspected members of the outlawed Kurdistan Workers Party (PKK) inside two flashpoint towns, security sources said on Thursday.

The operations conducted inside the towns of Cizre and Silopi in the southeastern Sirnak province, backed by curfews, mark a new escalation in five months of fighting with the PKK since a truce collapsed.

Mohammed, 22, has lived in Turkey for four years since fleeing Syria, just months after the civil war erupted that has torn his homeland apart.

But unlike hundreds of thousands of others who this year crossed the Aegean Sea in search of better lives in Europe, he has no plans to leave.

Turkish authorities have since September been detaining scores of refugees, including from Iraq and Syria, and abusing and pressuring them to return home in breach of international law, Amnesty International said Wednesday.

The government angrily rejected Amnesty's accusations, saying it "categorically denied" that any Syrian refugee in Turkey had been forced to return to their conflict-torn home.

The Iraqi government on Tuesday demanded the "complete withdrawal" of Turkish forces from its territory, indicating Ankara's partial pullout the previous day was not enough.

Turkey deployed soldiers and tanks to a military camp in northern Iraq earlier this month, a move it said was necessary to protect trainers at the site but which Baghdad condemned as an illegal incursion.

U.S. Defense Secretary Ashton Carter on Tuesday visited the Turkish air base near Syria that has become a key hub for American-led air raids against Islamic State jihadists.

Turkey earlier this year allowed U.S. forces to use the Incirlik base outside the southern city of Adana for bombing raids against IS targets in Syria. The Turkish air force later also joined the campaign.

Two protesters were killed Monday in clashes with police in Turkey's mainly Kurdish southeastern city of Diyarbakir amid growing tensions over a days-long curfew, security sources said.

The two demonstrators, aged 21 and 25, were shot dead in violent clashes that erupted over the curfew that has been in place in the city's central Sur district almost uninterrupted since December 2, a security source told AFP, asking not to be named.

A Russian-run energy company in Crimea said on Monday a Turkish vessel sparked an incident in the Black Sea last month by refusing to give way to a convoy of Russian ships.

The alleged incident took place on November 24, the company said, the same day Turkey shot down a Russian warplane on the Syrian border, leading to the biggest crisis in ties between the two countries since the end of the Cold War.

A Russian destroyer in the Aegean Sea on Sunday opened fire to avoid a collision with a Turkish fishing boat, the defense ministry said, as a bitter dispute over the shooting down of a Russian warplane raged on.

"The crew of the Russian patrol ship Smetlivy which was located 22 kilometers (13.7 miles) from the Greek island of Lemnos in the northern part of the Aegean Sea avoided collision with a Turkish seiner," the ministry said, adding that the crew had fired small arms to warn the boat.

Turkish authorities on Friday launched a new operation to arrest dozens of prominent suspects in a vast probe into the activities of a U.S.-based preacher who is the main foe of President Recep Tayyip Erdogan.

Prosecutors issued 65 arrest warrants, with raids carried out in Ankara, Izmir and several other cities, the official Anatolia news agency reported. 

Turkish Foreign Minister Mevlut Cavusoglu on Friday said Ankara's patience with Moscow after the downing of a Russian warplane on the Syrian border was "not unlimited", urging Moscow to react calmly.

"We are calling on Russia, our major trade partner, for calm. But we also say that our patience is not unlimited," Cavusoglu told the private NTV television in an interview.