Boris Johnson has been accused of "beating the drum for his own book sales" during an official visit to Serbia as Foreign Secretary.
During the visit last month he met Serbian Prime Minister Aleksandar Vucic and talked up joint efforts to tackle organised crime.
But at a stop in a Belgrade bookshop Mr Johnson discussed his book, The Churchill Factor, and even signed a number of copies, it has emerged.
The Guardian reported that Mr Johnson was "embarrassed" by the nature of the event and had asked for it not to be about the book, which was published last summer. The Foreign Office said press freedom was the planned subject of the talk.
Serbian media had nevertheless previewed the event as a discussion about the work, while its Serbian publisher tweeted about Mr Johnson's "brilliant remarks" during the bookshop visit.
Labour MP Andrew Gwynne, a shadow minister, said: "Boris Johnson’s responsibility is to lead the Foreign Office, not beating the drum for his own book sales.
"The Tories should focus on delivering for the country, sadly they’re more interested in furthering their own ends."
A Foreign Office spokeswoman said: "This was absolutely not a promotional event. The Foreign Secretary was invited to talk about freedom of the press at the oldest known bookstore in Belgrade.
"The store chose to welcome him by putting some of his books on display and some local people asked him to sign their books."
The spokeswoman later added that the bookshop was closed at the time of Mr Johnson's visit, and that he had spoken with a small number of journalists on the subject of press freedom.
It comes as Mr Johnson's proposed amnesty for illegal immigrants - which would allow them to stay if they have lived in the UK for 10 years - was shot down by Number 10 after he raised it during a Cabinet committee meeting.
Sources close to the Foreign Secretary were also forced to deny he had told at least four EU ambassadors that he privately supported freedom of movement, despite it not being part of the Government's Brexit policy.
The sources said the report was a "lie".
On Wednesday, Mr Johnson visited Cyprus, where he said that Brexit would not affect the UK's "deep historic ties" to the island. He also spent time with UN peacekeepers in the buffer zone in Nicosia.Reuse content