Police today posted photographs of the six -- four young males and two females -- who participated in the First Global Challenge robotics meet -- on Twitter.
"Two of the individuals were seen crossing over into Canada," said Karimah Bilal, a spokeswoman for police in the US capital.
"We have no indication of foul play," she said.
The Washington Post reported that the other four also were believed to be in safe hands, but Bilal said she had no information about their situation.
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It said it makes sure that all students get to their dormitory at Trinity Washington University after the daily competition.
They "are always to be under close supervision of their adult mentor and are advised not to leave the premises unaccompanied by the mentor," it said.
The international competition drew attention after US President Donald Trump intervened to allow an all-girl robotics team from Afghanistan whose members had been denied US visas to compete.
Between 500 and 2,000 people have been killed in clashes in the east African country, according to UN and NGO sources. More than 400,000 people have fled and dozens of opposition activists have been forced into exile.
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