Niinisto, who will be joined by foreign minister Pekka Haavisto, will discuss reconstruction efforts following the devastating earthquakes in February, "and Finland's and Sweden's NATO memberships", the president's office said in a statement.

Finland and Sweden dropped decades-long policies of military non-alignment and applied to join the western alliance last May in the wake of Moscow's invasion of Ukraine.

Turkey and Hungary are the only NATO members still to ratify the Nordic nations' applications, which must be accepted by all 30 existing members of the alliance.

Turkish President Recep Tayyip Erdogan has dug in against Sweden as he heads into a close presidential election, but Ankara looks ready to ratify Finland's membership.

However no ratification date has been set by Turkey's parliament with elections due May 14.

While Hungary's approval is also still needed, the path looks clear for Finland to join NATO before Sweden, even though the two countries coordinated their applications and stressed they wanted to join together.

Swedish Prime Minister Ulf Kristersson acknowledged Tuesday that the likelihood of Finland joining NATO before Sweden had "increased" in recent weeks, but stressed entry was just a matter of time.

Ankara suspended negotiations with Sweden after protests in January that included a Koran burning outside Turkey's embassy in Stockholm, but talks resumed in Brussels on March 9.