For the past two years, the Western defence alliance has navigated a challenging security environment in the face of Russia's invasion of Ukraine.

"I decided to enter the competition for the post of NATO secretary general," Iohannis, whose country borders Ukraine, told reporters.

Dutch Prime Minister Mark Rutte is largely believed to be the frontrunner to lead the alliance and replace Stoltenberg, after the United States, Britain and Germany expressed support for his potential candidacy.

Hungary, however, said the country would not support Rutte, who has previously criticised Hungary's government.

A successor for Stoltenberg -- the former Norwegian prime minister who has overseen NATO for a decade -- is expected to be announced before a July summit in Washington.

"Given the current security context, I believe it is time for our country to assume an even greater responsibility within the Euro-Atlantic leadership," Iohannis wrote in a statement.

He said Romania had a "deep understanding, including from the perspective of the historical challenges facing our region, of the current security situation, created by the war launched by Russia against Ukraine."

"At the same time, I believe that NATO also needs a renewal of the perspective on its mission," Iohannis added.

No decision is confirmed until consensus is reached on one candidate, according to NATO rules.