BUDAPEST — A bipartisan delegation of U.S. senators made an official visit to Hungary’s capital Sunday and called on the nationalist government to immediately approve Sweden’s request to join NATO. Hungary is the only one of NATO’s 31 existing members not to have ratified Sweden’s bid. The Hungarian government faces mounting pressure to act after delaying the move for more than 18 months since admitting a new country to the military alliance requires unanimous approval. The visiting senators announced they would submit a joint resolution to Congress condemning alleged democratic backsliding in Hungary and urging the government of Prime Minister Viktor Orbán to lift its block on Sweden’s trans-Atlantic integration. “With accession, Hungary and your prime minister will be doing a great service to freedom-loving nations worldwide,” Sen. Thom Tillis, a North Carolina Republican, said during a news conference at the U.S. Embassy in Budapest. The resolution, first reported early Sunday by The Associated Press, was authored by Tillis and Sen. Jeanne Shaheen, a New Hampshire Democrat. Joining them in the delegation to Budapest was Sen. Chris Murphy, a Democrat from Connecticut. Earlier this month, U.S. Sen. Ben Cardin, a Maryland Democrat and chair of the Senate Foreign Relations Committee, raised the prospect of imposing sanctions on Hungary for its conduct, and called Orbán “the least reliable member of NATO.” In the resolution, obtained by the AP, the senators note “the important role Hungary can have in European and trans-Atlantic security,” but point out its failure to keep earlier promises not to be the last NATO ally to sign off on Sweden’s membership. Hungary, the resolution says, “has not joined all other NATO member states in approving the accession of Sweden to NATO, failing to fulfill a commitment not to be last to approve such accession and jeopardizing trans-Atlantic security at a key moment for peace and stability in Europe.” Orbán, a staunch nationalist who has led Hungary since 2010, has said that he favors making Sweden part of NATO but that lawmakers in his party remained unconvinced because of “blatant lies” from Swedish politicians on the state of Hungary’s democracy. But in a state of the nation speech in Budapest on Saturday, Orbán indicated that Hungary’s legislature might soon relent. “It’s good news that our dispute with Sweden is nearing a conclusion,” he said. “We are moving toward ratifying Sweden’s accession to NATO at the beginning of the spring session of Parliament.” On Sunday, Shaheen said it was “disappointing” that no members of the Hungarian government had accepted invitations to meet the delegation, but that she was “hopeful and optimistic” that Sweden’s accession would be submitted for ratification on Feb. 26 when Hungarian lawmakers reconvene. Murphy said Orbán’s government’s refusal to meet was “strange and concerning,” but that the onus was on the long-serving leader to push forward a vote. “We are wise enough about politics here to know that if Prime Minister Orbán wants this to happen, then the parliament can move forward,” he said. The senators’ resolution criticizes Orbán’s increasingly warm relations with Russia and China, and notes that while Hungary has opened its doors to Ukrainian refugees fleeing Moscow’s invasion, it has also “resisted and diluted European Union sanctions with respect to the Russian Federation.” Orbán, widely considered to be the Kremlin’s closest EU ally, has long been criticized for flouting the bloc’s standards on democracy and the rule of law. The EU has withheld billions in funding from Budapest over alleged breaches of its rules. Hungary’s government has also adopted an increasingly adversarial stance toward the administration of President Joe Biden, accusing the U.S. of attempting to influence Hungarian public life. Péter Szijjártó, Hungary’s foreign minister, said Friday that he welcomed the senators’ visit but that it was “not worth trying to exert pressure on us, because we are a sovereign country.” “We are glad they are coming here because they can see for themselves that everything they read about Hungary in the liberal American media is a blatant lie,” Szijjártó said.