These countries have issued advisories about travelling to the U.S.

A number of tourists have been stopped at U.S. border crossings and held at U.S. immigration detention facilities for weeks.

Several European countries have added travel warnings for their citizens travelling to the United States in light of concerns they could face problems at the border because of the Trump administration’s policies.

Since U.S. President Donald Trump took office in January, he has signed executive orders that beefed up border policy, tightened the visa vetting process and cracked down on illegal migrants in the country.

In the wake of the stricter U.S. rules, citizens from other countries were refused entry or detained, including a Canadian. Vancouver entrepreneur Jasmine Mooney spent almost two weeks in various detention centres. Mooney was detained earlier this month after she applied for a visa at the U.S.-Mexico border, but she says she didn’t have much information on why she was jailed.

In another case, U.S. border officials on March 9 prevented a French space scientist from staying in the country to attend a conference and deported him, accusing him of writing “hateful” messages on his phone against U.S. policy, AFP reported.

United Kingdom

The U.K. government says its citizens should comply with all conditions of entry. It warned travellers that they may be arrested or detained if they break the rules, noting U.S. authorities “set and enforce” entry rules strictly.

Germany

Germany says in its travel advisory that a visa or entry waiver does not guarantee entry for its citizens. A foreign ministry spokesperson says Germany updated its travel advisory after several Germans were detained at the border.

Denmark

With Trump’s policies on transgender people sparking concerns, Denmark is advising residents who identify as transgender to contact the U.S. embassy in Copenhagen before visiting the United States.

Finland

After Trump signed an executive order stating that the country will recognize only the male and female sexes, Finland issued a similar warning to Denmark’s about travelling to the U.S.

Canada

The Canadian government on Friday updated its travel advisory for those visiting the U.S., as Canadians and other foreign nationals visiting for more than 30 days must register with the U.S. government. It’s advising travellers to visit the U.S. Citizenship and Immigration Services website for more details.

Canadian residents can check if they’re automatically registered by looking up their I-94 admission form on the U.S. Customs Border Protection website, according to the government.

“Failure to comply with the registration requirement could result in penalties, fines, and misdemeanor prosecution,” according to the advisory.

In addition, it said the government can’t intervene on Canadians' behalf if they don’t meet the entry or exit requirements.

U.S. border officials may also ask Canadians for additional information, such as proof of “residential, employment or educational ties” to Canada and proof of “sufficient funds” covering their stay.