President Recep Tayyip Erdoğan is expected to hold important face-to-face meetings with other world leaders to discuss bilateral ties and regional issues on the sidelines of a critical NATO summit in Madrid.

Erdoğan met with his French counterpart Emmanuel Macron early on Wednesday in Madrid for a closed-door discussion that lasted nearly an hour and kicked off the Turkish president's bilateral contacts at the high-level, three-day summit in the Spanish capital.

The two leaders discussed the importance of finding ways to let Ukraine export its grain, and ensuring security at the port of Odessa.

Macron also welcomed plans by Sweden and Finland to join NATO, added a statement from Macron's office.

Later, Erdoğan met with British Prime Minister Boris Johnson and European Council President Charles Michel.

Erdoğan also attended a family photo shoot at the NATO summit. The leaders posed for a family photo following the official welcoming ceremony at the IFEMA Convention Center in Madrid.

Ahead of the photo shoot, Erdoğan shook hands with Spain's Prime Minister Pedro Sanchez and NATO Secretary-General Jens Stoltenberg. In the photograph, British Prime Minister Boris Johnson stood to Erdoğan's right, while Slovenian Prime Minister Robert Golob stood to his left.

Later, the Turkish president shook hands with his U.S. counterpart Joe Biden, Johnson, Canadian Prime Minister Justin Trudeau, Albanian Prime Minister Edi Rama, and Stoltenberg and exchanged greetings. The leaders then moved on to the first session on Ukraine.

NATO leaders sat down Wednesday to try to turn an urgent sense of purpose triggered by Russia’s invasion of Ukraine into action and to patch up any cracks in their unity over money and mission.

Stoltenberg said the alliance was meeting in Madrid "in the midst of the most serious security crisis we have faced since the Second World War."

Russia’s invasion of its neighbor has shattered Europe’s peace and driven NATO to pour troops and weapons into eastern Europe on a scale not seen since the Cold War.

Members of the alliance have also sent billions in military and civilian aid to Ukraine. The 30 NATO leaders heard directly from Ukrainian President Volodymyr Zelenskyy, who asked them to do even more when he addressed the gathering by video.

Biden, whose country provides the bulk of NATO's military power, said the summit was sending "an unmistakable message ... that NATO is strong and united."

"We’re stepping up. We’re proving that NATO is more needed now than it ever has been," said Biden. He announced a hefty boost in America's military presence in Europe, including a permanent U.S. base in Poland, two more Navy destroyers based in Rota, Spain, and two more F-35 squadrons to the United Kingdom.

But NATO allies are showing signs of strain as the cost of energy and other essential goods has skyrocketed amid the war and tough Western sanctions on Russia. There also are tensions over how the war will end and what, if any, concessions Ukraine should make to stop the fighting.

The war has already triggered a big increase in NATO’s forces in Eastern Europe, and allies are expected to agree at the summit to increase the strength of the alliance’s rapid reaction force nearly eightfold, from 40,000 to 300,000 troops by next year. The troops will be based in their home nations but dedicated to specific countries on NATO’s eastern flank, where the alliance plans to build up stocks of equipment and ammunition. Stoltenberg said NATO was undertaking "the biggest overhaul of our collective defense since the end of the Cold War."

Meanwhile, NATO leaders adopted a new strategic concept on Wednesday that describes Russia as "the most significant and direct threat to allies' security and stability", reflecting a grave deterioration in the alliance's relations with Moscow over the past decade.

In 2010, when leaders agreed the alliance's last master document setting out its vision for NATO, they aimed to build a long-term partnership with their old Cold War adversary. Dmitry Medvedev, Russia's president at the time, was present at the Lisbon summit where it was agreed.

China was not even mentioned in the 2010 strategy, seen in the West as a benign trading partner and manufacturing base. It is now described as a challenge to NATO's "interests, security and values", as an economic and military power that remains "opaque about its strategy, intentions and military build-up".

For the first time, the leaders of Japan, Australia, South Korea and New Zealand are attending the summit as guests, a reflection of the growing importance of the Indo-Pacific region. Stoltenberg said China was not NATO’s adversary, but posed "challenges to our values, to our interest and to our security."

The summit opened with one problem solved, after Turkey agreed Tuesday to lift its opposition to Sweden and Finland joining NATO. In response to the invasion, the two Nordic nations abandoned their long-held nonaligned status and applied to join NATO as protection against an increasingly aggressive and unpredictable Russia – which shares a long border with Finland.

NATO operates by consensus, and Ankara had threatened to block the Nordic pair, insisting they change their stance on some groups that Turkey considers terrorists. After urgent top-level talks with leaders of the three countries, alliance chief Stoltenberg said the impasse had been cleared.

The 30-nation alliance issued a formal invitation Wednesday to the two countries to join. The decision has to be ratified by all individual nations, but Stoltenberg said he was "absolutely confident" Finland and Sweden would become members. Stoltenberg said he expected the process to be finished "rather quickly," but did not set a time.

"The accession of Finland and Sweden will make them (the allies) safer, NATO stronger and the Euro-Atlantic area more secure," a communique published by the NATO summit in Madrid on Wednesday said.

After the announcement, Stoltenberg thanked Turkey, Finland and Sweden for accepting his invitation "to engage in negotiations to find a united way forward."

"This is a good agreement for Turkey, Finland and Sweden, and it is a good agreement for NATO," he said.