David Cameron's description of Nigeria and Afghanistan as "fantastically corrupt" has been branded "embarrassing" and "unfair" by the two countries on the eve of their leaders' visit to the UK.
Cameron was caught on camera making the unflattering comment during a conversation with the Queen ahead of an anti-corruption summit which he is hosting in London on Thursday.
Labour accused the PM of having "egg on his face", but Downing Street downplayed the significance of the remarks - pointing out that the presidents of both countries had acknowledged the scale of the problem they faced.
Afghanistan's Ashraf Ghani and Nigeria's Muhammadu Buhari are due to attend the London summit and each has written an essay for an accompanying book, discussing their efforts to tackle graft in their countries.
According to extracts released by Number 10, Ghani acknowledges in his piece that Afghanistan is "one of the most corrupt countries on earth" and Buhari that corruption became a "way of life" in his country under "supposedly accountable democratic governments".
Cameron was caught on a broadcast camera chatting with the Queen, Archbishop of Canterbury Justin Welby and Commons Speaker John Bercow at a Buckingham Palace event to mark the monarch's 90th birthday.
"We've got some leaders of some fantastically corrupt countries coming to Britain," Cameron told the Queen. "Nigeria and Afghanistan - possibly the two most corrupt countries in the world."
Buhari's spokesman Garba Shehu later released a statement on social media: "This is embarrassing to us, to us say the least, given the good work that the president is doing. The eyes of the world are on what is happening here. The prime minister must be looking at an old snapshot of Nigeria. Things are changing with corruption and everything else."
And a spokesman for the Afghan embassy in London said: "President Ghani and his government since in office have taken major steps to fight corruption. Countering corruption is a top priority along security issues for the National Unity Government.
"We have made important progresses in fighting systematic capture in major national procurement contracts and are making progress on addressing institutional issues as well as issues related to impunity. Therefore calling Afghanistan in that way and taking bold decisions by NUG is unfair."
Labour likened the episode to a previous occasion when Cameron was caught by a TV microphone revealing how the Queen "purred" with pleasure when he told her Scots had rejected independence.
"This is another gaffe from the PM - you'd hope he'd have learned his lesson when it comes to off the record comments and the Queen but sadly not," MP Wes Streeting said.
In the footage, the Archbishop - who has considerable experience of Nigeria from his time as an oil executive - is heard to intervene to say that "this particular president is actually not corrupt ... he's trying very hard", in an apparent reference to Buhari. Cameron responds: "He's really trying."
Bercow is also heard making a joke about the summit, quipping: "They are coming at their own expense, one assumes?"
After some laughter, Cameron answers: "Yes ... because it's an anti-corruption summit, everything has to be open, so there are no sort of closed-door sessions, it's all in front of the press."
Anti-corruption movement Transparency International ranked Afghanistan as 166th and Nigeria 136th out of 168 countries and territories in its Corruption Perceptions Index for 2015.
