The UK government confirmed Wednesday it had detained an unspecified number of migrants in recent days for deportation to Rwanda in July under its controversial new policy.
It comes a week after lawmakers ended months of parliamentary wrangling and passed a law allowing some asylum seekers to be deported by declaring Rwanda to be a safe third country.
The new legislation circumvented a Supreme Court ruling last year that sending migrants to Rwanda in this way would be illegal because it "would expose them to a real risk of ill-treatment".
Prime Minister Rishi Sunak has vowed to stop migrants arriving on small boats from mainland Europe. He vowed last week to begin detaining people promptly before deportation flights start within "10 to 12 weeks".
Reports of immigration enforcement officers holding people earmarked for the flights emerged earlier this week. On Wednesday, the interior ministry confirmed that "a series of nationwide operations" was underway.
"The first illegal migrants set to be removed to Rwanda have now been detained," it added.
Calling it "another major milestone" in the Rwanda plan, the ministry released photographs and a video of immigration enforcement officers detaining several migrants at different residences.
They were seen being led away in handcuffs and put into secure vehicles.
A spokesman for Sunak said the UK leader was pleased that "the first detentions have taken place.
"It's obviously an important part of now operationalising the plan to get flights off the ground in nine to 11 weeks time and provide the effective deterrent that we need to stop seeing these dangerous boat crossings," he added.
A senior minister said Tuesday the government expected to deport 5,700 migrants to Rwanda this year, after the interior ministry confirmed that Kigali had "in principle" agreed to accept that number.
Of those, 2,143 "can be located for detention" before being flown there, the ministry said, leaving more than 3,500 currently accounted for.
Ministers have insisted the enforcement teams will find them.
The government has increased detention capacity to more than 2,200 spaces ahead of the first Rwanda flights, it said Wednesday.
Commercial charter planes have also been booked and an airport has been put on standby, it added.
On Tuesday, London also confirmed that the first failed asylum seeker had travelled to Rwanda under a separate voluntary scheme.
Rwanda, home to 13 million people in Africa's Great Lakes region, claims to being one of the most stable countries on the continent and has drawn praise for its modern infrastructure.
But rights groups accuse veteran President Paul Kagame of ruling in a climate of fear, stifling dissent and free speech. UK opposition parties, UN agencies and French President Emmanuel Macron have also criticised the Rwanda scheme.
Sunak's ruling Conservatives argue the threat of being deported to Rwanda will deter tens of thousands of annual cross-Channel arrivals, and insist the policy is already having an impact.
But the main Labour opposition has repeatedly dismissed it a "gimmick" that will not stop the cross-Channel arrivals.
Official statistics show arrivals have increased by more than a quarter in the first third of the year compared to the same period in 2023.