NATO head Jens Stoltenberg said Tuesday the "morally totally unacceptable" bombardment of the Syrian city of Aleppo broke international law, and urged Russia to take genuine steps to restore a ceasefire.

Russia's defense minister on Wednesday rebuked NATO for bolstering its military presence in eastern Europe and vowed Moscow will take countermeasures.

Britain will remain a strong ally and continue to play a leading role in NATO despite its vote to leave the European Union, alliance head Jens Stoltenberg said Friday.

NATO chief Jens Stoltenberg on Wednesday demanded that Russia withdraw its forces and military hardware from Ukraine, and halt its support for pro-Moscow separatists battling Kiev.

NATO will send units to Romania, alliance head Jens Stoltenberg said Tuesday, on top of battalions being deployed in the three Baltic states and Poland in response to Russia's intervention in Ukraine.

NATO will deploy four international battalions to Poland and the three Baltic states as part of the wider pushback against Russia's intervention in Ukraine, alliance head Jens Stoltenberg said Monday.

In its new mission in the Aegean to help Europe tackle its worst migration crisis in 60 years, NATO is wading into one of the world's most contested seas.

The Aegean has claimed the lives of hundreds of migrants in the past year, including scores of children. It has also been a habitual source of tension between NATO members Greece and Turkey for decades.

NATO will take any request to help with the refugee crisis "very seriously", chief Jens Stoltenberg said Tuesday after Germany and Turkey sought the alliance's assistance in combating human smugglers.

Defense ministers from the 28-nation group will discuss the issue at a meeting in Brussels Wednesday and Thursday when they review NATO's response to a more assertive Russia and the security threat posed by the Syria crisis.

The top NATO commander in Afghanistan on Tuesday denied reports that the Pentagon had ordered U.S. troops to ignore the sexual abuse of young boys by Afghan police and militias.

The New York Times reported Sunday that U.S. troops in Afghanistan had been instructed by their superiors to overlook cases of Afghan police or commanders sexually abusing teenage boys, even if it took place on military bases.

Russia is still sending weapons to separatist rebels battling the Ukrainian government despite a fresh truce in the war-torn east of the country, NATO chief Jens Stoltenberg said Monday.

"The ceasefire is mainly holding. This is, of course, encouraging because that was not the case before," Stoltenberg said on the first day of a visit to Ukraine.