President Biden on Monday offered an awkward fist-bump to Turkish President Recep Tayyip Erdogan in Belgium at the annual NATO summit Monday — as the Islamist strongman prepared to blast the U.S. leader for his recent recognition of the Armenian genocide.

Biden, wearing a mask despite being fully vaccinated against COVID-19 for months, approached an unmasked Erdogan, who was seated at a desk, and offered his fist at an angle that caught the Turkish leader off guard.

Erdogan rose to greet Biden, continuing the casual knuckle contact as they spoke. 

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Erdogan and Biden later sat down for a more formal meeting. But in a surprise twist, U.S. reporters who were supposed to be in the room were left waiting in a hallway.

Confirmation of the Biden-Erdogan sit-down came through Erdogan’s press office, which tweeted images of Biden and Erdogan bumping wrists and smiling at one another. In one image, Erdogan flashed a thumbs up.

The U.S.-Turkish relationship has been roiled in recent years, including by Erdogan’s militarism in Syria and Libya and his suppression of dissent following an alleged coup attempt in 2016.

In April, Biden recognized as a genocide the World War I slaughter of Armenians by Turks and Kurds, angering the Turkish leader. Last year, Biden called on Erodgan to abandon his decision to turn the Hagia Sophia, a former Christian church, from a museum into a mosque.

Ahead of the NATO summit, Erdogan made it clear that he would confront Biden over his stance on the Armenian genocide, saying the designation "disturbed and upset" Turkey.

"An ally country taking such a stance on an issue that has nothing to do with NATO, the issue of Armenians, has disturbed and upset us. It is not possible to go on without reminding (Biden of) this," Erdogan said.

Erdogan, in power since 2003, notoriously watched in 2017 as his guards attacked U.S. citizens near the White House after a meeting with then-President Donald Trump. Fifteen of his guards faced U.S. charges, though charges against 11 of them were dropped in 2018. Congress blocked an arms sale to Turkey after the attack.

Although a NATO ally, Trump in 2018 ordered sanctions against Turkey’s interior and justice ministers over the detention of U.S. pastor Andrew Brunson, who ultimately was released.

In 2019, Turkey attacked U.S.-allied Kurds in northern Syria after Trump announced plans to draw down U.S. troops there. Trump warned Erdogan not to be a "tough guy" or "fool", but Erdogan ignored him and launched the attack.

U.S. President Joe Biden, right, is greeted by Turkey's President Recep Tayyip Erdogan, center, during a plenary session at a NATO summit in Brussels, Monday, June 14, 2021. (AP Photo/Olivier Matthys, Pool)

In 2020, the U.S. sanctioned Turkey for purchasing for $2.5 billion S-400 surface-to-air missiles from Russia.

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The U.S. has repeatedly refused Erdogan’s request to deport Turkish cleric Fethullah Gulen, who lives in Pennsylvania. Erodgan claims Gulen was behind the 2016 coup attempt.

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