BERLIN - Germany updated its travel advisory for the United States to emphasize that a visa or entry waiver does not guarantee entry for its citizens after several Germans were detained at the border recently, a foreign ministry spokesperson said.

The ministry updated its travel advice website for the US on Tuesday to clarify that neither approval through the US ESTA system nor a US visa entitles entry in every case.

"The final decision on whether a person can enter the US lies with the US border authorities," said the spokesperson on Wednesday.

However, the spokesperson emphasized that the change did not constitute a travel warning.

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Since taking office on January 20, US President Donald Trump has announced a number of immigration-related executive orders that focus on stricter border policy, tighter visa vetting procedures and a crackdown on undocumented migrants in the United States.

Germany's foreign ministry said earlier this week that it was monitoring whether there had been a change in US immigration policy after three nationals had been detained.

Two of the three cases have been resolved, with the affected nationals returning to Germany, while the remaining case was being handled with the help of the consulate general in Boston.

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According to Boston-based public broadcaster WGBH, a German man with a green card residency permit was detained by immigration authorities this month at Boston airport and was being held in a detention facility.

The German foreign ministry did not immediately respond to a request for information about the man's current whereabouts.