Hungary's ruling party on Tuesday said it would call for a parliamentary vote on Monday to ratify Sweden's NATO accession bid.

The move would bring an end to more than 18 months of delays by the nationalist government that have frustrated Hungary's allies.

In a letter on Tuesday to the speaker of the parliament, the head of the Fidesz caucus, Mate Kocsis, requested that a vote be scheduled for the opening day of the spring session, which begins Monday.

Kocsis wrote that Fidesz, which has repeatedly blocked a vote on the matter, will opt to support Sweden's bid to join the trans-Atlantic military alliance.

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 1 1/2-year since admitting a new country to the military alliance requires unanimous approval.

On Sunday, a bipartisan group of U.S. senators visited Hungary and announced they would submit a joint resolution to Congress condemning alleged democratic backsliding in the country and urging Prime Minister Viktor Orban to move forward on approving Sweden's accession as soon as possible.

Sen. Chris Murphy, a Democrat from Connecticut, said in Budapest on Sunday that members of the Hungarian government and Fidesz had refused to meet with the delegation – something he called "strange and concerning" – but said that the onus was on the long-serving leader to push for a vote.

"We are wise enough about politics here to know that if Prime Minister Orban wants this to happen, then the parliament can move forward," he said.

Orban has faced isolation over his obstruction of key decisions by his international allies, including putting up roadblocks to EU funding for cash-strapped Ukraine. But in a state of the nation speech in Budapest on Saturday, Orban 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."

Reacting to the news of the vote, Sweden's Defense Minister, Pal Jonson said in Stockholm that Sweden "naturally welcome this."

"It is of course very welcome," Jonson said.