New Delhi, Turkey has made it clear that unless the security concerns raised by it are addressed with "concrete steps within a timeframe", it won't let Finland and Sweden join North Atlantic Treaty Organization (NATO) - the transatlantic military alliance of 30 North American and European countries.

Even though the United States believes that there is a very "strong consensus" in NATO for the admission of Finland and Sweden, the entire process has hit a major roadblock with Ankara asking for elimination of the "terrorist threats" -- majorly those associated with the Kurdistan Workers' Party (Kurdish acronym PKK) - originating from these countries first.

"For as long as Tayyip Erdogan is the head of the Republic of Turkey, we definitely cannot say 'yes' to countries which support terrorism entering NATO," country's President Recep Tayyip Erdogan told accompanying media while returning from Azerbaijan over the weekend.

Erdogan once again reiterated that Turkey could not have a positive view on the NATO membership of the two countries so long as terrorists are "still walking the streets of Stockholm" and Sweden is protecting them "with its own police".

"They are not honest or sincere. We cannot repeat the mistakes made in the past on (admitting) countries that embrace and feed such terrorists into NATO, which is a security organization," the Turkish President was quoted as saying by Daily Sabah,Turkey's leading newspaper.

Erdogan's comments come after delegations from Sweden and Finland landed in Ankara last week to seek support from the key NATO member which has the second largest number of military personnel in the Alliance.

During the meeting, Turkey raised security concerns related to the presence of PKK, PYD, YPG, DHKP-C and FETO separatist groups which continue to be active in European countries.

Following the discussions, Turkey's Presidential Spokesperson Ibrahim Kalin detailed that his country has so far made 28 extradition requests from Sweden and 12 from Finland, "none of which have been responded to in the affirmative" till date.

"In short, we have strongly underlined that there is a need for a change of mentality and paradigm. We have clearly conveyed our message that the process will not progress unless Turkey's security concerns are addressed with concrete steps within a timeframe," said Kalin.

Meanwhile, Washington, which fully supports Finland and Sweden joining the Alliance, continues to make frantic efforts to end the stalemate in view of the ongoing Russia-Ukraine conflict.

After his meeting with Finnish Foreign Minister Pekka Haavisto in Washington on Friday, US Secretary of State Antony Blinken said that he remains confident all parties involved will work through the process swiftly as there is a very strong consensus in NATO for the admission of Finland and Sweden.

"The most important thing is that Finland and Sweden are speaking directly to and with Turkey, and working through some of the concerns that Turkey has raised and finding ways to address them. We very much support that process; as I mentioned, we're engaged with Turkey directly as well," said Blinken.

However, with negotiations making a little headway, all eyes are now fixed on the NATO Summit in Madrid (June 28-30) where the issue is likely to dominate the proceedings.

Spanish PM Pedro Sanchez, who will be hosting the crucial gathering where NATO will adopt its new Strategic Concept, has already confirmed that the leaders of Sweden and Finland will be in attendance at the meet.