President Recep Tayyip Erdogan of Turkey signed the protocol approving Sweden’s bid to join the NATO military alliance and sent it to the Turkish Parliament on Monday, according to a brief statement from his office.

It was not immediately clear why Mr. Erdogan, who had refused to officially endorse Sweden’s NATO bid for many months, suddenly decided to back it now, nor when Parliament would vote on it. Parliamentary approval is the final step in the process.

After Russia’s invasion of Ukraine last year, Sweden and Finland, which both have borders with Russia, applied to join NATO, a process that is subject to approval by all of the alliance’s members.

Mr. Erdogan initially refused to back either of them, but later changed his stance on Finland, paving the way for it to join NATO in April. But he continued to hold out on Sweden, accusing it of not doing enough to crack down on Turkish separatists and other Turkish dissidents in Sweden that Turkey considers terrorists.

NATO spokesmen declined to comment on Monday, noting that Secretary General Jens Stoltenberg would be in Stockholm on Tuesday to meet with the Swedish prime minister, Ulf Kristersson, and would likely address the issue there.

Hungary is the only other NATO nation that has not approved Sweden’s membership bid, although Hungarian officials have said they would follow Turkey’s lead.

Lara Jakes contributed reporting.