As the number of confirmed cases of the Omicron coronavirus variant rose to 160 in Britain, the government on Saturday announced further tightening of travel restrictions to combat its spread.

Beginning Tuesday, travelers will be required to take a coronavirus test within 48 hours of traveling to Britain regardless of their vaccination status, and imposed restrictions on travelers from Nigeria, the country’s health secretary said in a statement. Nigeria announced on Wednesday that it had detected the variant in three travelers who arrived from South Africa in November, according to Dr. Ifedayo Adetifa, the director general of the Nigeria Centre for Disease Control.

The two additional measures being imposed by Britain are the latest to come after a week of heightened concern led to the introduction of a number of restrictions intended to slow the incursion of the Omicron variant.

At the moment, travelers are required to self-isolate and take a coronavirus test on the second day after arriving. If that test is negative, they can end their isolation. If not, they are expected to remain in self-isolation until they do get a negative result.

There are now 160 confirmed cases of the Omicron variant across Britain, Britain’s Health Security Agency confirmed on Saturday, up from 134 cases reported by the agency on Friday. Britain is considered a leader in genomic sequencing and testing, with a well-run national program to track coronavirus mutations, so it has an advantage in tracking the variant’s spread.

“We’ve kept the data under review over the last week or so since we learned about Omicron,” Sajid Javid, the country’s health secretary, said during a news briefing. “And we’re seeing an increasing number of cases linked to travel.”

He stressed that the new containment measures are temporary, but he added that “before we learn more about Omicron, it’s right that we have these measures in place.”

Mr. Javid was also clear that the government was advising the British public to continue with life as usual while adhering to coronavirus guidelines.

“People should carry on with their plans, and make plans to enjoy Christmas as usual,” he said.