Biden is to meet with Prime Minister Rishi Sunak and King Charles III
US President Joe Biden has landed in the UK ahead of a Nato summit in Lithuania later this week - which comes after several allies questioned his call to send cluster bombs to Ukraine.
The UK and Canada are among those who voiced concern about supplying the bombs, which are widely banned because of the danger they pose to civilians.
The US says they are needed because Ukraine's weapon stocks are dwindling.
The presidential plane touched down at Stansted Airport on Sunday evening.
On Monday, Mr Biden will meet British Prime Minister Rishi Sunak to discuss various issues, including the war in Ukraine.
Mr Sunak has not directly criticised his US counterpart following Friday's cluster bomb announcement - but on Saturday he said that the UK was one of 123 countries signed up to the Convention on Cluster Munitions, an international treaty which bans the production or use of the weapons.
Other US allies have gone further, however. Nato partner nation New Zealand said on Sunday the munitions could cause "huge damage to innocent people".
Cluster bombs typically release lots of smaller bomblets that can kill indiscriminately over a wide area.
Unexploded bomblets can linger on the ground for years before they detonate.
The US says it has received written reassurances from Kyiv that Ukrainian troops will not use the weapons in Russia or in urban areas.
While in the UK, Mr Biden will also meet King Charles III for the first time since the King was crowned.
Members of Nato - a military alliance of 31 Western nations - will then meet in Vilnius on Tuesday and Wednesday.
Finland will attend its first summit since joining in April. Plans from Sweden to follow suit have been blocked by Turkey, which accuses it of harbouring terrorists.
Mr Biden is expected to seek further support from Mr Sunak to help broker a deal with Turkey.
The matter is also expected to be on Nato's agenda in Lithuania - along with boosting ammunition stockpiles and reviewing defence plans.
Ukraine harbours its own ambitions of joining Nato. But speaking to CNN before his trip, Mr Biden said this could not happen until the war was over - in line with the alliance's long-standing policy.
Joe Biden in UK to meet Sunak and King Charles amid Ukraine concerns
The US president is facing criticism over his decision to send the controversial weapons to Ukraine.
www.bbc.co.uk
