CONSTANTA: NATO Secretary-General Jens Stoltenberg said on Friday that the presence of American troops in Romania showed the United States' commitment to the security of Europe, as more soldiers arrived at an airbase.

Stoltenberg, speaking alongside Romania's president, also reiterated his concerns about a possible Russian invasion in Ukraine and said the alliance would consider a longer-term presence in south-eastern Europe in the coming months.

NATO chief says Russian build up at 'dangerous moment'

"We continue to reinforce our eastern flank," Stoltenberg said, stressing that NATO's actions were defensive.