U.S. President Joe Biden is in London for an overnight stop Sunday enroute to Lithuania for the NATO summit in Vilnius, where it remains unlikely that the alliance will welcome Sweden as its 32nd member due to persistent objections from Turkey.

During the flight to Britain, Biden spoke on the phone with Turkish President Recep Tayyip Erdogan for a last-minute push to pave the way toward Ankara agreeing to Sweden’s accession — a process that must be unanimous among all current members.

“I can’t characterize how close, how far, all I can say is that we believe that Sweden should be admitted to NATO as soon as possible,” White House national security adviser Jake Sullivan told VOA aboard Air Force One enroute to London. “We believe that there should be a pathway to do so.”

In a readout of the call, Ankara stated that Sweden has taken some steps in the right direction but has not made sufficient progress to support Stockholm’s application to join NATO.

Ankara has accused Sweden of being too lenient toward militant Kurdish organizations that Turkey considers terrorist groups. Following Turkish demands, Sweden has enacted reforms, including a new anti-terrorism law. Erdogan initially accused Finland of doing the same but approved Helsinki’s application to join NATO in April.

Sullivan added that Biden and Erdogan discussed the sale of F-16s, a subject that remains a sticking point for Ankara despite its public denials. In its statement, Ankara noted Erdogan said “it would be incorrect to associate Sweden’s NATO accession with the sale of F-16 jets” while thanking Biden for his support to Ankara on its desire to purchase the fighter planes.

Lawmakers from both parties in the U.S. Congress, which has authority to approve major weapon sales, insist that Ankara must first drop its objections to Sweden’s accession before the deal can proceed.

Hungary also opposes Sweden’s bid but has said it will approve it if Turkey assents.

Biden, British leaders to meet

On Monday Biden will meet with British Prime Minister Rishi Sunak and King Charles to discuss various bilateral issues and climate financing for developing nations.

It will be Biden and Sunak’s sixth meeting in six months. In June, Biden hosted Sunak at the White House, committing to the Atlantic Declaration to cooperate on advanced technologies, clean energy, and critical minerals to counter China’s clout around the world.  

Biden heads to Vilnius Monday evening for a two-day meeting with NATO leaders where they will discuss bolstering support for Ukraine, which includes hashing out the final wording of a compromise communique that will signal to Kyiv it is moving closer to membership without promises of a quick accession. He has repeatedly said Ukraine must make additional reforms to qualify for NATO membership.

In an interview taped last week, Biden told CNN he thinks it is premature to call for a vote on Ukraine joining NATO.

“I don’t think it’s ready for membership in NATO,” Biden said. “I don’t think there’s unanimity in NATO now …in the middle of a war. If the war is going on [and Ukraine was a NATO member], then we’re all in the war. We’re at war with Russia,” since NATO’s charter calls for all its members to defend any individual country when it is attacked.

Allies will also discuss security guarantees for Kyiv outside of the NATO framework as it moves toward membership. Sullivan said that Washington alongside allies and partners within a multilateral framework will negotiate long-term bilateral security commitments with Ukraine.

“Meaning that the United States would be prepared to provide in various forms of military assistance, intelligence and information sharing, cyber support and other forms of material support, so that Ukraine can both defend itself and deter future aggression,” he said.

NATO countries, led by the United States, have sent billions of dollars in armaments to Ukraine, but Russian aerial bombardments have continued to kill dozens of Ukrainian civilians even as Kyiv’s forces have shot down hundreds of incoming missiles. The ones that landed have killed people and destroyed residential buildings.

Next stop: Helsinki

After the NATO summit, Biden heads to Helsinki, the Finnish capital, to commemorate Finland recently joining the military alliance created in the aftermath of World War II, and to meet with Nordic leaders.

Finland joined NATO in April, effectively doubling the length of Russia’s border with the world’s biggest security alliance. Biden has characterized the strengthened NATO alliance as a sign of Moscow’s declining influence.

White House correspondent Anita Powell and VOA’s Ken Bredemeier contributed to this report.