The Turkish president reiterated his opposition to Finland and Sweden joining NATO - just hours after they announced their bid for membership.
Recep Tayyip Erdogan said the two Scandinavian countries should not bother sending delegations to persuade Turkey, a key member of NATO, with their bids.
He is angry at what he sees as a willingness to host Kurdish militants.
Without the support of all NATO members, Sweden and Finland could not join the military alliance.
Sweden said on Monday that Europe is experiencing a dangerous new reality, referring to the Russian invasion of Ukraine.
Russian President Vladimir Putin said that led to a response from the Kremlin.
At a press conference on Monday, Erdogan said Turkey opposes Finland and Sweden's efforts to join NATO, describing Sweden as a "breeder" for terrorist organizations.
"None of these countries have a clear and open attitude toward the terrorist organization. How can we trust them?" The Turkish president said.
Turkey accuses the two northern countries of harboring members of the Kurdistan Workers Party, a group it considers a terrorist organization, and followers of Fethullah Gulen, whom Ankara accuses of orchestrating the 2016 coup attempt.
All member states must agree that a new country can join NATO, and thus Sweden and Finland are asking for Turkey's support in their attempt to join the military alliance.
Erdogan said that the Swedish and Finnish delegations should not bother going to Ankara, the capital of Turkey, to persuade them to agree to the NATO file.
His government also pledged to block requests from countries that have imposed sanctions on it.
In 2019, the two Scandinavian countries imposed an arms embargo on Ankara after its incursion into Syria.
Finnish Foreign Minister Pekka Haavisto, speaking in parliament in Helsinki on Monday, said he was surprised by Turkey's position, but added that his government was not interested in "compromising" with Erdogan.
Finland officially announced its bid to join NATO last week.
Neighboring Sweden joined it on Saturday in a move that would end centuries of the Scandinavian country's military disalignment.
"NATO will strengthen Sweden, and Sweden will strengthen NATO," Prime Minister Magdalena Andersson said at a press briefing on Monday.
She said that Europe is now experiencing a dangerous new reality, referring to the Russian invasion of Ukraine.
"We are leaving one era behind and entering a new era," Anderson told lawmakers during a debate in Stockholm on Monday.
She said the official application could be delivered within several days and would be synchronized with Finland. NATO has expressed its willingness to accept the two new members.