The two Nordic states applied last year to join the North Atlantic Treaty Organization (NATO) following Russia's invasion of Ukraine but their bids must be approved by all 30 NATO member states. Turkey and Hungary have yet to endorse the applications.

On Monday, Turkish President Tayyip Erdogan said the two countries had to deport or extradite up to 130 "terrorists" to Turkey before parliament would approve their bids to join NATO.

Turkey has said Sweden in particular must first take a clearer stance against what it sees as terrorists, mainly Kurdish militants and a group it blames for a 2016 coup attempt.

"At expert level the discussions are going well .. and the cooperation goes well but we still see a lot of heated debate on this issue," Finland's Foreign Minister Pekka Haavisto told Reuters on the sidelines of the World Economic Forum in Davos.

The U.S., a key broker in the NATO talks, has told Congress it is preparing the potential $20 billion sale of F-16 fighter jets to Turkey, sources familiar with the matter told Reuters. Some have speculated that should the deal go ahead Ankara would soften its resistance to the Nordic bids.

Turkish Foreign Minister Mevlut Cavusoglu is set to visit Washington on Wednesday.

"The U.S. cannot solve all the problems but it would be a good sign if Turkey and the U.S. can agree on this military package they are planning," Haavisto said. "If there is a green light on that package, hopefully it helps the Swedish and Finnish membership of NATO."

Finland and Sweden signed a three-way agreement with Turkey in 2022 aimed at overcoming Ankara's objections.

Swedish Foreign Minister Tobias Billstrom said that Ankara had had legitimate security demands, but those had been met and it was now time to ratify the Nordic NATO membership bids.

"We believe we have now reached a point where Sweden and Finland have done what we committed ourselves to in this (trilateral) memorandum," Billstrom told Reuters in an interview.

"We believe very strongly that we have done what was being asked and we do not see any reason for the ratification not to start."

(Reporting by John Irish; additional reporting by Anne Kauranen, Editing by Alexandra Hudson)

By John Irish