NATO Secretary-General Jens Stoltenberg said Sunday that Turkey has "legitimate concerns" over terrorism and other issues that need to be taken seriously.
Turkey has accused Finland and Sweden of supporting Kurdish militants and says it will not back the two Nordic nations joining NATO until they change their policies.
Speaking at a joint news conference with Finnish President Sauli Niinisto, Stoltenberg stressed that "no other NATO ally has suffered more terrorist attacks than Turkey" and pointed to its strategic geographic location with neighbors like Iraq and Syria.
"These are legitimate concerns. This is about terrorism, it's about weapons exports," Stoltenberg said. "We have to address the security concerns of all allies, including Turkish concerns about the terrorist group PKK."
He spoke at Finland's presidential summer residence Kultaranta in western Finland.
After decades of military non-alignment, Russia's war in Ukraine pushed Finland and Sweden to apply to join NATO in May. Turkish President Recep Tayyip Erdogan, however, accuses the Nordic nations of supporting Kurdish militants deemed by Turkey to be terrorists and has vetoed their entry into the 30-member alliance.
"When a vital key ally as Turkey raises concerns on terrorism then of course we have to sit down and take them seriously. And that's exactly what we do," Stoltenberg said.
The demands from Ankara to Helsinki and Stockholm also include lifting restrictions on arms exports to Turkey and extraditing members of certain Kurdish organizations that are opposed to Erdogan's government.
In the past weeks, NATO's chief has been trying to resolve the dispute but he did not disclose Sunday whether any progress has been made.
He was to attend an annual discussion panel in Kultaranta later Sunday together with Finnish and Nordic politicians, foreign and security policy experts and military representatives.
Stoltenberg will visit Sweden on Monday for talks with the Swedish Prime Minister Magdalena Andersson.