Japan's government said Friday it will extend the quarantine period for travelers who have recently been to Britain from three days to six days next week to prevent the spread of the highly contagious coronavirus variant first found in India.

Those who have been to Britain within 14 days of arrival will be required to stay at a government-designated facility and be tested twice for coronavirus starting from Monday, the government said.

Travelers from the European country will join those arriving from other countries, such as India and Bangladesh, subject to an extended quarantine as Japan has been strengthening its border controls.

"We will flexibly take necessary measures from the standpoint of protecting the health and lives of the people," said Chief Cabinet Secretary Katsunobu Kato in announcing the new measure.

The British government has been planning to lift COVID-19 restrictions in England on June 21, but the outlook has become increasingly uncertain with the recent spread of the variant in the country.