U.S. Secretary of State Hillary Rodham Clinton has said that NATO should enlarge at the alliance's next summit.
Clinton spoke during a NATO summit in Chicago on May 21, at the start of a meeting with aspiring members Bosnia-Herzegovina, Georgia, Macedonia, and Montenegro.
Clinton said, "I believe this summit should be the last summit that is not an enlargement summit."
The next NATO summit has yet to be scheduled.
Clinton maintained that prospective members must fulfill the required criteria for joining the alliance.
"As with any country that wishes to join NATO, we look to them to demonstrate that they share our values,: she said. "And [that] they are willing and able to meet the standards for membership, and we promise to help them as they do so, because this is in our interests."
Clinton also emphasized that expansion should strengthen the alliance.
"We know it can be a lengthy and challenging process, but we need to stick with it," she said, adding that the "ultimate goal" was a "stronger, more durable, [and] more effective NATO."
NATO Secretary-General Anders Fogh Rasmussen said NATO and the four nations aspiring to join it shared "common security concerns."
"The nations around this table, allies and partners, share common security concerns. And it is right that we develop common approaches to deal with those concerns. Today’s meeting will offer us the opportunity to share views, to discuss what we have done well, and where we can do more," Rasmussen said ahead of the meeting with the four NATO aspirants.
Macedonia is closest to NATO accession, held back only by a dispute with NATO-member Greece over the name of the country.
Georgia has also made progress toward membership in the alliance, but is still expected to resolve differences with neighboring Russia.
The two countries fought a war in August 2008, after which Russia recognized the breakaway Georgian regions of South Ossetia and Abkhazia as independent.
Bosnia and Montenegro are working on implementing reforms required by the 28-member alliance.
The Chicago summit declaration praised the aspirant countries for their contributions to NATO operations, but failed to offer concrete hopes for membership.
The last round of NATO enlargement came in April 2009 when Albania and Croatia joined the alliance.
With reporting by dpa