US President Joe Biden said in a phone chat on Monday that Turkish President Tayyip Erdogan reiterated Ankara’s desire to acquire F-16 fighter planes from the US, and that Washington wants Ankara to withdraw its opposition to Sweden joining NATO.

The encounter occurred on Sunday, when Biden contacted Erdogan to congratulate him on his victory in Turkey’s presidential election.

“I talked to Erdogan.” Erdogan was congratulated by me. He still wishes to work on something involving F-16s. I told him we needed to make a deal with Sweden, so let’s get it done. So we’ll keep in touch,” Biden said to reporters before leaving the White House for Delaware.

Asked if he expected any movement from Erdogan on Sweden’s NATO membership, Biden said: “I raised that issue with him. We’re going to talk more about it next week.”

Sweden and Finland applied for NATO membership last year, ditching long-held policies of military non-alignment following Russia’s invasion of Ukraine. Bids for membership must be approved by all NATO members. Turkey and Hungary have yet to approve Sweden’s bid.

Turkey has sought to buy $20 billion worth of F-16s and nearly 80 modernization kits from the United States. But the sale has been stalled due to objections from the U.S. Congress over Ankara’s refusal to green light to NATO enlargement, its human rights record and Syria policy, even though the Biden administration has repeatedly said it supports the sale.

A much smaller $259 million package including avionics software upgrades for Turkey’s current fleet of F-16 fighter aircraft was cleared by U.S. Congress earlier this year, days after Turkey ratified Finland’s NATO accession.

The Biden administration has repeatedly rejected any assertion of any “quid pro quo” between the sale and the NATO enlargement, although Turkish Foreign Minister Mevlut Cavusoglu in January said the U.S. side made it clear that an approval of NATO bids would be viewed positively by the Congress.

A bipartisan group of senators in a February letter to Biden said Turkey’s failure to ratify the accession protocols for Sweden and Finland, which was still waiting at the time, would “call into question this pending sale”, referring to the F-16s.

A source familiar with the discussions said the United States had previously told Turkey it would be hard to get Congress to approve the F-16 deal if Ankara doesn’t green light Sweden.

Turkey ratified Finland’s NATO accession in late March, but has continued to object to Sweden, saying Stockholm harbors members of militant groups it considers to be terrorists. Hungary has also not yet approved Sweden’s bid.

Seeing Sweden join NATO by mid-July when the alliance is due to hold a leaders summit in Lithuania is among the top priorities for Washington.

The Turkish Presidency in a statement on the call between Biden and Erdogan said the two leaders agreed to deepen cooperation on all aspects of their bilateral ties, which have grown in importance in the face of regional and global challenges.