The Russian foreign minister Sergei Lavrov has been taken to the hospital after his arrival for the G20 summit in Bali, Indonesian authorities said.
Three Indonesian government and medical officials said he was being treated on the resort island.
Two said Mr Lavrov was being treated for a heart condition.
The officials said he was taken to Sanglah Hospital in the provincial capital, Denpasar, but the hospital did not immediately comment.
The Russian foreign ministry dismissed the development as “fake news”.
In a Telegram post, director of the information and press department for the ministry Maria Zakharova said: “We can’t believe our eyes: it turns out that he is hospitalised. This is, of course, the aerobatics of fakes. Well, wait, world exclusive.”
Mr Lavrov is the highest-ranking Russian official attending the G20 summit which begins on Tuesday.