Kiev and Warsaw on Wednesday disagreed on whether the one million Ukrainians living in Poland were refugees or economic migrants, as Europe tackles an unprecedented immigration crisis.

Polish Prime Minister Beata Szydlo, whose conservative Law and Justice (PiS) party has been reluctant for Warsaw to take in its share of those fleeing unrest in Syria and elsewhere, set off the spat with remarks Tuesday. 

A trial opens Wednesday of a New York police officer accused of manslaughter over the death of an unarmed black man, whose shooting fueled nationwide protests against U.S. police tactics.

Rookie officer Peter Liang, 28, will stand trial for manslaughter in the second degree, criminally negligent homicide, assault in the second degree, reckless endangerment and two counts of official misconduct.

Macedonia has closed its border with Greece to migrants, police in Skopje said Wednesday, blocking the path of hundreds trying to reach northern Europe.

"The border is closed," a senior Macedonian police official told AFP, while a police spokesman in northern Greece said it had been closed since Tuesday evening, leaving about 600 migrants stranded at the frontier.

U.N. Security Council ambassadors headed to Burundi on Wednesday to push the government to open up serious talks with the opposition and agree to an African Union force that could prevent a slide to all-out war.

It is the second time in less than a year that the 15-member council travels to Burundi, where the United Nations has warned that months of violence could escalate into ethnic killings and mass atrocities.

Turkish President Recep Tayyip Erdogan on Wednesday launched a blistering attack on academics who criticized his policies in the Kurdish-dominated southeast, warning they would pay a price after falling into a "pit of treachery."

Prosecutors have launched a major investigation against more than 1,200 Turkish academics who signed a petition denouncing the military operations against Kurdish rebels in the southeast.

A German court on Wednesday began the trial of an Islamic State "storm trooper" who allegedly helped track down deserters for the jihadist group in Syria.

Nils D., a 25-year-old German national, had traveled to Syria in October 2013, where he "took on several tasks within the Islamic State organization," prosecutor Carola Bitter said.

A Turkish court on Wednesday remanded in custody pending trial two more suspects over a suicide bombing blamed on the Islamic State (IS) group that killed 10 German tourists in Istanbul last week, reports said.

A court in Istanbul placed the suspects -- who were detained in southeastern city of Sanliurfa on Saturday -- under arrest on charges of "premeditated murder and membership in a terror group", the Anatolia news agency reported.

European Union ambassadors on Wednesday expressed concern about the closure of the offices in Sudan of a UK-based Christian NGO that has worked in the country for more than a decade.

"The ambassadors of the resident EU embassies and Norway in Khartoum follow with great concern the reports of the closure of offices of Tearfund," the EU delegation in Khartoum said in a statement.

A Mauritanian al-Qaida jihadist, on death row until his escape on New Year's Eve, was re-arrested on Tuesday night after crossing the Guinea-Bissau border into Guinea, security sources said Wednesday.

"Cheikh Ould Saleck, was on the run for three weeks, and from Mauritania entered Senegal then Guinea-Bissau," a high-ranking police source who asked not to be identified told AFP.

NATO is discussing whether to invite Russia to their first formal talks since 2014, aiming to put ties damaged by the Ukraine crisis back on an even keel, diplomatic sources said Wednesday.

Despite their differences both sides recognized the need for "transparency", the sources said, against a backdrop of a series of crises including Ukraine and the war in Syria.