"We should sell them the F-16 jets and modernise those jets as well," Biden said, adding there was "no quid pro quo" linking the sale to Turkey's approval for Finland and Sweden entering NATO.

Biden added that for the sale, "I need congressional approval to do that and I think I can do that".

The declaration of support from Biden comes after Turkey surprised fellow NATO members at a summit in Madrid by suddenly dropping weeks of opposition to the Finland and Sweden applications to join the alliance.

Unanimous consent by NATO members is required for enlargement.

Turkish President Recep Tayyip Erdogan said he would send a delegation to the United States "without delay" to convince lawmakers to swiftly approve the sale.

"It's necessary to get support from both Democrats and Republicans. Despite all this, Mr Biden is confident. I hope that we will get a result that fits our friendship and solidarity," Erdogan told a news conference in Madrid.

Turkey is an important NATO member in a strategically sensitive location, but it has had often tense relations with its European partners and Washington, which is the alliance's main military force.

"In politics, yesterday was yesterday, today is today," Erdogan said.

"In politics, a lot can change in 24 hours... There were good days and bad days but Turkish-US relations have continued," he said.

A plan to equip Turkey with state-of-the-art US F-35 stealth fighters fell through after Turkey bought Russia's S-400 anti-aircraft missile system.

Washington saw Ankara's purchase as potentially threatening the security of the F-35 programme.

Turkey next set out to buy new F-16s, as well as obtaining upgrades for its existing, but outdated fleet of the same planes.

However, that deal is also on hold and there has been speculation that Turkey was holding up the NATO accession bids of the two northern European countries to try and leverage concessions.