The talks in Lithuania Monday are a last-ditch attempt to convince Turkish leader Recep Tayyip Erdogan to drop his objections after over a year of delays before NATO leaders gather.

"It is absolutely possible to have a positive decision at the summit next week," Stoltenberg said after talks with Sweden and Turkey's foreign ministers at NATO's Brussels headquarters.

Sweden's Foreign Minister Tobias Billstrom said he was hoping for a breakthrough but underscored it remained a "Turkish decision".

"We believe from our point of view we have fulfilled all our commitments," he said.

NATO allies have been pressuring Ankara for months to give way and let the Scandinavian nation in by the time of the two-day summit starting Tuesday in Vilnius.

Turkey and Sweden inked a deal aimed at clearing the path to accession at a NATO summit over a year ago.

Ankara has demanded a Swedish crackdown on Kurdish movements, such as the the Kurdistan Workers' Party (PKK), which it says is a terrorist group.

Sweden says it has made good on the deal.

On Thursday it jailed a Turkish citizen for "attempted terrorist financing" for the PKK under new legislation.

But Erdogan has continued to criticise Stockholm, and a protest last week that saw pages of the Koran burnt further stoked his ire.

"Any further delay in Sweden's membership would be welcomed by the PKK and (Russian) President (Vladimir) Putin," Stoltenberg said.

US President Joe Biden is expected to make a strong push for Sweden in the coming days.

Biden told Sweden's prime minister at a meeting in Washington on Wednesday that he was "anxiously looking forward" to the country joining.

Sweden and its neighbour Finland dropped decades of military non-alignment and applied to join NATO in the wake of Russia's invasion of Ukraine.

Finland formally joined the bloc in April.

Hungary is also still holding out on Sweden's membership, which requires the unanimous approval of all 31 NATO members.

But Budapest has indicated it will give way if Turkey agrees.