2 Police Officers Killed In Russia's Karachai-Cherkessia

"By this summer, when we get to the Washington summit, we expect to have roughly two-thirds of the alliance meeting the target," Smith said on May 16 in an interview with RFE/RL.

NATO members Croatia, Albania, Montenegro, and North Macedonia in particular were urged "to work harder to try and hit the 2 percent target" by the time the NATO summit takes place, she said.

"They have all worked tirelessly over the last decade to increase their defense spending, and we salute those efforts," Smith said.

"Those are difficult national decisions to make that are hard when there are demands on the domestic side of the house to spend money on other priorities."

President Joe Biden is hoping to celebrate the largest number of allies at 2 percent than seen over the last decade at the July 9-11 summit, she said.

"So, anything that our friends in the Western Balkans can do to increase that defense spending would be appreciated. And it's not just because of burden sharing, but it's because of the current security environment," Smith said. "There are threats all around us."

She cited the war in Ukraine, Russia's evolving partnership with China, its increased defense production, and the support Russia is receiving from Iran and North Korean.

"There are so many reasons for us all to increase our defense spending. And we really want to get to a situation where every member of this alliance spends 2 percent," she said.

The alliance has come a long way since making the 2014 pledge when only three members spent 2 percent of GDP on defense. That has grown to 18, according to NATO Secretary-General Jens Stoltenberg in an interview with RFE/RL in February.

Smith agreed that three other Balkan non-NATO members -- namely Kosovo, Bosnia-Herzegovina, and Serbia -- have a special relationship with alliance.

Bosnia is a "full-fledged aspirant" that has openly stated a desire to join, and all 32 ambassadors recently traveled to Bosnia to talk about what more could be done to deepen the partnership, help Bosnia transform and modernize its forces, and work on interoperability.

Serbia has its own sovereign decision to make on whether or not it wants to pursue membership, Smith said.

"Right now, the answer coming from Serbia is no. But they do have a partnership with the alliance where we are able to…train with them [and] work with them on any specific needs that they have when it comes to cybersecurity or work on modernizing their forces. They can determine how they want to work with the alliance."

Kosovo is more complicated, because four NATO countries do not recognize its independence.

"But the United States has a very close partnership with Kosovo, and we are not only supporting the EU-led, facilitated dialog that is working towards normalization between Kosovo and Serbia, but from a U.S. bilateral perspective, we are here to support our friends in Kosovo as they work towards their own Euro-Atlantic aspirations and work to strengthen their forces as well."

Asked about U.S. concerns over about Serbia's purchase of military equipment from China and Russia, Smith said the United States had been very clear.

"They should tread lightly and be cautious about working with [Chinese-]owned companies. We believe there are risks and challenges in doing so, and we also do not believe that this is the time for any country to be deepening its relationship with Russia," she said.

The United States has delivered "frank and open messages" in conversations with Serbia, but also recognizes that it is their own sovereign decision.

She also warned against Russian influence and disinformation, saying the United States encourages its friends in the Western Balkans to stay focused on the values they share with the West and their Euro-Atlantic aspirations.

"Russia is doing its very best to put out, a whole sea of disinformation campaigns that often misrepresent what NATO is about," she said. "They often try to make the claim that NATO is directly engaged in the war in Ukraine, which is preposterous and not true."

Russia puts out falsehoods about what NATO does in the Western Balkan region and refuses to acknowledge that NATO is a defensive alliance, she said.

"It is, in fact Russia that is the aggressor in the case of Ukraine. Russia started this war in Ukraine and of course it could end it tomorrow if it so desires," she said.