WASHINGTON -- Two of six Burundi teenagers who went missing after an international robotics competition in the United States have been seen crossing the border into Canada, U.S. authorities said Thursday.

The search for the teens is ongoing, but police have no indication of foul play in their disappearance, said Aquita Brown, a spokeswoman for police in Washington, D.C.

Canadian officials would not say if the two students reported to have been seen crossing the border -- a 16-year-old and a 17-year-old -- had made refugee claims.

Canada Border Services Agency said in an email Thursday that it is not its practice to confirm or deny the entry of any person into Canada. The RCMP said it was not in a position to comment on the matter.

American authorities tweeted missing person fliers Wednesday asking for help finding the six teens, who had last been seen in the U.S. at the FIRST Global Challenge around the time of Tuesday's final matches. The missing team members include two 17-year-old girls and four male students ranging in age from 16 to 18.

The competition in the U.S. capital, which is designed to encourage youths to pursue careers in math and science, attracted teams of teenagers from more than 150 nations. A squad of girls from Afghanistan drew the most attention after they were twice rejected for U.S. visas and President Donald Trump intervened.

Organizers learned Tuesday night that the Burundi team's mentor couldn't find the six students who participated in the competition and FIRST Global president Joe Sestak made the initial call to police, a FIRST Global Challenge statement said.

The mentor said the teens travelled from Burundi for the competition and have one-year visas, U.S. police reports say. The mentor said they disappeared after the competition, but he doesn't know where they went. The reports say police tried to contact one missing teen's uncle but got no response.

The competition's webpage about Team Burundi shows the six team members posing with a flag and says team members were selected from schools in Bujumbura, the capital city.

Alastair Clarke, a Canadian immigration lawyer based out of Winnipeg, said one of the most common reasons asylum-seekers choose Canada over the U.S. is because of a "general fear of the Trump administration."

"I have heard it on numerous occasions that individuals have chosen Canada because they don't feel that the U.S. government is supportive of refugees," said Clarke, who has worked on several cases involving Burudi refugees claimants.

He said many refugees claimants in the U.S. are detained while their asylum claims are in process and many have heard that they will receive more legal support and support from established communities in Canada.

"I've had clients who have gone through the U.S. system and they have been detained for four, six, 12 or 18 months while their refugee claim is in process," Clarke said. "This has been a huge detriment to their application -- they have not had access to counsel, they have not had access to get proper documents."

Clarke added that Burundi -- an East African nation of about 10 million people who speak the local Kirundi language and French -- is on a list of countries at the Refugee Protection Division for expedited processing.

Henry Chang, a Toronto-based lawyer for Blaney McMurtry, who is not involved in the situation, said the one-year visas issued to the students by the U.S. government mean they would likely fall under the Canada-U.S. Safe Third Country Agreement.

The agreement requires people to apply for asylum in the first country where they arrive, unless an immediate family member lives in the other country.

The Canadian government has faced pressure to repeal the agreement, with many arguing it is the reason asylum-seekers have crossed the border on foot, to bypass border points so they could make their refugee claims once already in the country.

"There is a clear perception ... that Canada is more inclined to grant them refugee status if they come here," Chang said. "That's why you've seen this influx of people -- who aren't even illegal, they are in legal status -- but they don't think there is any hope for them in the U.S., so they make the trek across the border like everyone else is doing right now."

-- With files from Daniela Germano at The Canadian Press