(Reuters) – U.S. law enforcement authorities on Friday were seeking six teenagers from Burundi who went missing after a robotics competition in Washington, two of whom had been spotted crossing the border into Canada.

The teens, aged 16 to 18, were last seen Tuesday after the FIRST Global Robotics Challenge, Washington, D.C., police said.

“We have been in touch with the Metropolitan Police Department; they told us that they are doing what they can to find those teens,” Benjamin Manirakiza, first counselor in the Burundi Embassy in Washington, said in a phone interview on Friday. “We have confidence in the capacity of the police.”

A Washington police spokeswoman said the teenagers’ disappearance was still under investigation on Friday, and declined to say what U.S. state they were spotted crossing from.

Police have said they do not believe foul play was involved.

Two of the teens – Audrey Mwamikazi, 17, and 16-year-old Don Ingabire – were spotted crossing the United States border into Canada. The other missing Burundians were named as Nice Munezero, 17; Kevin Sabumukiza, 17; Richard Irakoze, 18; and Aristide Irambona, 18.

Officials at Canada’s Border Services Agency, the immigration and refugee ministry and the Burundian embassy in Ottawa, said they had no information on the teens’ whereabouts.

The Royal Canadian Mounted Police declined to comment on the teens’ whereabouts but said that anyone who crossed the border illegally would be returned to border services.

“Crossing the Canadian border without reporting at a port of entry is illegal,” said spokeswoman Annie Deslile, in an e-mail. “If the individual who has illegally entered between ports of entry claims to be a refugee, he/she is then transported to a port of entry.”

High school students from more than 150 countries took part in the competition, which was designed to encourage careers in math and technology. An all-girl squad from Afghanistan drew worldwide attention when President Donald Trump intervened after they were denied U.S. visas.

Burundi has long been plagued by civil war and other violence. Fighting has killed at least 700 people and forced 400,000 from their homes since April 2015 when President Pierre Nkurunziza said he would run for a third term in office.

FIRST Global, a U.S. non-profit that organized the competition, said it had notified police about the missing competitors.

More than 3,000 would-be refugees have crossed the U.S. border into Canada so far this year, according to government statistics.