Sweden and Finland applied to join the transatlantic alliance in the wake of Russia's invasion of Ukraine.

"We think that NATO is a group of 30 democratic countries with common values and very strong transatlantic cooperation, and this is what we are looking for at this moment," Haavisto added.

Turkey's foreign ministry said presidential spokesman Ibrahim Kalin and deputy foreign minister Sedat Onal will meet the Finnish-Swedish officials on Wednesday.

Turkish Foreign Minister Mevlut Cavusoglu was quoted as saying by private broadcaster NTV that Ankara has prepared a "draft agreement" that will be the basis of the discussions. Turkey wants "guarantees" that can be made in an official, signed agreement, not "wishes", he said.

NATO member Turkey has long accused Nordic countries, in particular Sweden which has a strong Turkish immigrant community, of harbouring outlawed Kurdish militants as well as supporters of Fethullah Gulen, the US-based preacher wanted over a failed 2016 coup.

President Recep Tayyip Erdogan warned Saturday that Turkey would oppose membership for the two applicants unless its concerns were addressed -- potentially a major obstacle as a consensus is required in NATO decisions.

"We understand that Turkey has some of their own security concerns, such as terrorism," Haavisto said.

"We think that we have good answers for those because we are also part of the fight against the terrorists. So, we think that this issue can be settled," he added.

Beyond smoothing ruffles between the Nordic countries and Turkey, analysts say Ankara may be making a show of opposition to secure concessions from other NATO members, such as deliveries of fighter planes from the United States.

Haavisto said "there might be also some issues that are not linked directly to Finland or Sweden more to other NATO members or so forth, but I'm sure that in a good spirit, NATO can solve this issue."