A bipartisan U.S. Congressional delegation will visit Hungary on Sunday as pressure grows on Budapest to ratify Sweden's NATO membership when parliament reconvenes after its winter break.

Hungary is the only NATO country not to ratify Sweden's application, a process that requires the backing of all members, souring relations with the United States and raising concerns among its allies.

Sweden applied to join NATO in May 2022 in a historic shift in policy prompted by Russia's invasion of Ukraine.

Hungarian Prime Minister Viktor Orban, who has better ties with Russia than other EU states and most NATO members, says his government backs Sweden joining the alliance, but the legislation nevertheless remains stranded.

The U.S. Embassy said in a statement on Friday the senators would travel to Hungary "on a mission focused on strategic issues confronting NATO and Hungary".

Sweden's NATO accession is an issue that directly affects the United States' national security and also the security of the alliance as a whole, U.S. Ambassador David Pressman said this month.

Sweden's NATO bid could be ratified when parliament reconvenes in late February, the ruling Fidesz party's parliamentary group has said. Sweden's foreign minister said on Wednesday that he expects that Hungary to approve the application soon. (Reporting by Krisztina Than; Editing by Nick Macfie)