NATO will consider a long-term presence in south-eastern Europe in the coming months, NATO Secretary-General Jens Stoltenberg said.

His remarks came during a speech at the Mihail Kogalniceanu military base in Romania.

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

He said the presence of US troops in Romania demonstrated the United States' commitment to the security of Europe.

Along the eastern flank, from the Black Sea to the Baltics, NATO allies have deployed additional forces and equipment. Stoltenberg explained that it was a necessary defensive response to the Russian troop build-up on the border with Ukraine.

The total number of US troops in Romania is nearly 2,000.

Next week, NATO defense ministers will meet to discuss possibilities to strengthen presence on the eastern flank, including with new battlegroups.