U.S. Secretary of State Rex Tillerson has written to the leaders of the U.S. Senate urging them to approve Montenegro's bid to join NATO, saying it is "strongly in the interest of the United States," media reported.
In a March 7 letter, Tillerson argued that Montenegro's membership in the military alliance would support greater integration, democratic reform, trade, security, and stability in the Balkans, Reuters reported on March 21.
Objections from two Republican senators, Rand Paul and Mike Lee, have delayed a vote in the Senate for months.
Paul has questioned the wisdom of angering Russia, which opposes the expansion of NATO, and has objected to the costs of approving NATO membership for a tiny country that he said could not play a significant role in defending the United States.
Montenegro, with a population of 650,000, hopes to win the required approval of all 28 NATO allies in time to become a full member at a NATO summit in May. It has been approved by 24 members.
NATO members see Montenegro's accession as a way to counter Russia's efforts to expand its influence in the Balkans -- a view expressed by Tillerson, who urged the Senate to act before the May summit, which President Donald Trump plans to attend.
"Montenegro's participation in the May NATO summit as full member, not as an observer, will send a strong signal of transatlantic unity," Tillerson wrote.
"It is strongly in the interests of the United States that Montenegro's membership in NATO be ratified."