Alok Sharma’s intervention is the latest sign of divisions at the top of Ms Truss’s administration.
It emerged this week that Downing Street has advised the King against travelling to Sharm el-Sheikh for the follow-up to the COP26 gathering in Glasgow last year, which was addressed by the Queen.
No 10 has yet to confirm whether the prime minister will attend the summit, where progress will be sought on agreements to stem the climate crisis achieved at Glasgow.
Now COP26 president Mr Sharma has said both PM and King should be in Egypt, amid fears of a poor turnout by world leaders reflecting a shift in attention away from global warming as a result of the Ukraine crisis.
Mr Sharma told The Times: “I would like the prime minister to go to COP27. It would cement the leadership position that the UK has on this incredibly important world issue.
“I would certainly welcome the king’s attendance at COP27. I know that many people around the world see him as a leader in this area.”
He rejected any suggestion that attendance at the summit would drag the King into politics, saying: “This is absolutely an issue that transcends politics. I mean, this is ultimately about ensuring that we protect our planet for future generations.”
Fomer UN climate chief Patricia Espinosa told the paper it was vital that the world shows “unity of purpose” in Egypt.
She said that progress is “very clearly not good”, particularly when it came to a commitment of greater ambition to curb emissions.
COP26 was attended by world leaders from US President Joe Biden to India’s Narendra Modi. Nearly 200 countries committed to upgrading their emissions plan in 2022, to put the world back on track for the 1.5C climate goal it set under the Paris Agreement.
But Mr Sharma said: “The report card since COP26 is that we made some progress, but not enough. We need to go further and faster.”