UK nationals visiting India this month will have to undergo mandatory quarantine even if they are fully vaccinated against COVID-19 in retaliation for UK curbs on Indian citizens.
The new rules, which take effect from Monday, follow the UK decision to require Indians vaccinated with AstraZeneca's Covishield to quarantine.
India mainly relies on the Covishield vaccine, developed by AstraZeneca and manufactured in India by Pune-based Serum Institute, which is not recognised by Britain under new rules, despite being identical to the doses given to millions of Britons.
AstraZeneca is one of the key providers to Britain's vaccination programme, along with US peers Moderna and Pfizer.
"India has decided to impose reciprocity on UK nationals arriving in India from the UK," the source said, declining to be identified in line with government policy.
Government sources in New Delhi had last month warned of retaliation after Foreign Minister Subrahmanyam Jaishankar said he had urged for an early resolution after a meeting with his British counterpart at the United Nations General Assembly in New York.
US Secretary of State Marco Rubio said on Thursday that the United States remains prepared to play a "constructive role" in helping bring an end to the war in Ukraine, following talks with Russian Foreign Minister Sergei Lavrov on the sidelines of an ASEAN gathering in Manila.
Indian Prime Minister Narendra Modi said on Thursday that "fast-track" courts would be set up to prosecute those behind exam paper leaks, his first public response after days of youth protests demanding the resignation of the education minister.
The US House of Representatives narrowly passed its version of a massive defence policy bill, despite Democrats' concerns about its huge price tag, the Iran war and a provision that would boost Pentagon ties to Israel.
At least seven more bodies were recovered from the tunnel of an under-construction hydroelectric project in India's northeastern state of Sikkim, the state government said on Thursday, bringing the death toll from a blast to 22.