South Sudan’s government demanded an explanation on Monday after the Sudanese national anthem was mistakenly played instead of their own during a basketball match at the Paris Olympics.

The incident occurred just before South Sudan’s opening men’s basketball game against Puerto Rico, which resulted in a historic victory for the East African nation.

South Sudan’s team became the first African side to win their opening match against a non-African team, defeating Puerto Rico 90-79.

The incorrect anthem played for nearly 20 seconds, leading to boos from fans of both teams and visible frustration among South Sudanese players.

Organizers had played the national anthem of neighboring Sudan instead of South Sudan’s “South Sudan Oyee.”

South Sudan gained independence from Sudan in 2011 following years of civil war, and disputes over borders and resources have continued to cause clashes between the two nations.

During a parliamentary session in Juba on Monday, Deputy Foreign Minister Semaya K. Kumba expressed disappointment at the error, calling it “unacceptable” that the Sudan national anthem was played.

“We have taken a formal kind of disappointment to the international community of the Olympics, and we have received a verbal apology,” Kumba said.

“But I would like to say that all of us here, there’s nobody and nobody that can accept that.”

The government has contacted the International Olympic Committee (IOC) through its embassy in Paris to seek clarification on how the mistake happened and to prevent similar incidents in the future.

On Sunday, South Sudan made history by becoming the first African team to defeat a non-African opponent at the Olympics, beating Puerto Rico 90-87 in their Group C game.

The team is set to face the United States on Wednesday, with a potential quarter-final berth on the line.