The Hungarian parliament is set to hold an extraordinary sitting at the opposition's request Monday to debate Sweden's NATO bid, although the ruling party plans to boycott the session.

Budapest remains the last holdout to ratify the Nordic country's bid to join the military alliance, following Turkey's ratification in January.

Hungary has maintained close ties with the Kremlin after its invasion of Ukraine in February 2022, and while it has said it supports the Swedish bid in principle, it has been dragging its feet for months.

Prime Minister Viktor Orban is delaying the vote due to his "personal vanity", Agnes Vadai from the biggest opposition party told AFP.

Orban seeks to "make headlines in the international press, while making a gesture to Russian President Vladimir Putin by undermining the unity of NATO and the EU," she said.

The United States has ramped up pressure on Hungary to ratify Stockholm's bid.

On Friday, the US embassy publicly reminded Orban that he promised to act "at the first opportunity" and "Monday's session provides him with one", it said in a statement.

Co-chairs of the US Senate's NATO Observer Group warned that "both time and patience are wearing thin."

Orban has invited his Swedish counterpart to Hungary, citing the need to "build strong mutual trust" through "more intense political dialogue".

Sweden's Prime Minister Ulf Kristersson accepted the invitation, but rejected the idea of "negotiations" and "demands" concerning the country's bid to join NATO.

Members of the Fidesz-KDNP ruling coalition -- which has an absolute majority in parliament -- have signalled they "are waiting for the Swedish Prime Minister to visit Hungary" before they finish ratification during the regular legislative session.

"If this is an important issue for the Swedes, the Swedish Prime Minister will obviously come to Budapest," Fidesz wrote in a statement sent to AFP.

Parliament is due to reconvene on 26 February, and ratification could take place quickly once it has received Viktor Orban's approval.

Turkey's parliament last month ratified Sweden's NATO membership after more than a year of delays that upset Western efforts to show resolve in the face of Russia's war on Ukraine.

NATO membership applications require unanimous ratifications by all alliance members.