Mo Farah has stepped up his criticism of Donald Trump’s attempt to impose a travel ban on people from mainly Muslim countries, calling it “crazy and unfair”, and still has concerns about how he will be treated when he returns home to the United States.

The double 5,000m and 10,000m Olympic champion, who was born in Somalia – one of the seven countries named in the president’s executive order last month – also revealed he had been scared when he heard about Trump’s plans while at his training base in Ethiopia and felt it was important to keep raising the issue on behalf of innocent people whose voices were not being heard.

“It was crazy and unfair,” Farah said. “That’s why I stood up and spoke out. They have made changes for people like me but the hard part was living in the US for six years and going to a training camp and hearing the news I can’t go back and see my kids. That was scary and it was important for me to speak out as there are a lot of innocent people out there who couldn’t say anything.”

The executive order was blocked by the courts but Trump’s threat to push through a revised version as early as next week has Farah concerned. “I’m not a politician and as an athlete you don’t like to get involved in politics but sometimes when it affects you – it affected me and my family – you have to speak up,” he said. “And a lot of people got behind me.”

Farah, who will compete in the 5,000m at the Indoor Grand Prix in Birmingham on Saturday, also said he had worries over whether he would be stopped and interrogated by border guards when he returned to his home in Portland, Oregon. “Yes, I’ve had issues before,” he said. “Hopefully it will be fine, and I always try to look on the bright side of life. But I go back in March and see my family and at that point we will see.”

Farah nodded when the 110m world record holder, the American Aries Merritt, who is also competing in Birmingham on Saturday, gave an eloquent condemnation of Trump’s behaviour as president. “The way his administration has been running is not normal,” Merritt said. “We have seen a lot of deceit, a lot of lies and slander and it’s not something that makes me proud to be an American at this point. But hopefully Congress and the Senate will keep him in check as best as they can.”

For now Farah’s primary focus is on his first race since finishing a sluggish seventh at the Edinburgh International XCountry last month. He believes he will be more like his old self following four weeks of hard grind in Ethiopia when he faces a field who include the Scot Andrew Butchart, who was sixth over 5,000m at the Rio Olympics.

“Edinburgh was not what I wanted,” Farah said. “It was a wake-up call to get back into full training. Sometimes you have to be honest with yourself, rewind and refocus. I had a little bit of break after Rio and spent time with my kids and family but I needed to be back training and pushing myself. At Edinburgh I wasn’t quite ready.

“There are a lot of athletes out there who are training hard and want to beat you so you’ve got to go back to basics and training camp. The last four weeks have been hard work and I’ve been cranking up the miles, so it will be nice to see where I am, but I’m definitely in better shape.”

Farah could find himself eclipsed by Laura Muir, who has her eye on a world record when she competes over the little-run 1,000m distance. The 23-year-old from Scotland has set a British 5,000m and a European 3,000m record indoors on the track this winter and is targeting Kelly Holmes’ British best of 2:32.55 set in 1997, as well as Maria Mutola’s world mark of 2:30.94.

“It will be a great opportunity and I can’t believe I’m at the standard that it can be a possibility,” Muir said. “I’m really looking forward to the weekend and seeing what I can go out there and do.”

The British 100m and 200m record holder, Dina Asher-Smith, who fractured her foot in training on Thursday, will not compete. She is another high-profile absentee after Katarina Johnson-Thompson withdrew and had been expected to take on the Olympic 100m and 200m champion, Elaine Thompson, and the world indoor 60m champion, Barbara Pierre.

Asher-Smith tweeted: “Last session before the grand prix, last reactive jump, and I land awkwardly on my foot and fracture it. What are the odds? Gutted!”