Prime Minister David Cameron and The Prince of Wales, representing the Queen, are flying to Saudi Arabia following the death of King Abdullah bin Abdulaziz.
They will join a host of international dignitaries in Riyadh to pay their respects to the Saudi royal family.
President Obama is to cut short his visit to India in order to fly to Saudi Arabia, a long-standing ally of the US.
Mr Obama will travel to Riyadh on Tuesday to meet King Salman, the White House confirmed.
King Abdullah, 90, died on Thursday evening after almost two decades leading the world's biggest oil exporter.
Both Mr Cameron and the Queen said they were "saddened" by his death.
The PM's decision to fly to Saudi comes amid sharp criticism over a decision to lower flags at Whitehall and across England as a mark of respect for the late monarch.
Downing Street and Whitehall buildings, including Westminster Abbey and Buckingham Palace, were instructed by the Department for Culture, Media and Sport on Friday to lower the Union Flag for 12 hours in tribute.
Some politicians and human rights campaigners have criticised the tributes to Abdullah who presided over a country where a woman was recently beheaded in public, a blogger was sentenced to receive 1,000 lashes for 'insulting Islam' and where women have been banned from driving.
Ruth Davidson, leader of the Scottish Conservatives, dismissed the flag tribute as "a steaming pile of nonsense", adding that it was "a stupid act on its own and a stupid precedent to set".
Former Conservative MP for Corby, Louise Mensch, took to twitter to vent her anger: "It is so unacceptable to offer deep condolences for a man who flogged women, didn't let them drive, saw guardian laws passed and starves them."
She even tweeted "F*** YOU" in reply to a tweet from the British Embassy in Riyadh which quoted the Prime Minister's sorrow at the king's death.
The head of Amnesty International, Salil Shetty, said: "The Saudi regime seems insensitive to human rights and human dignity and unfortunately they are also protected by many Western countries because they have oil and because they are seen as allies in the fight against terrorism."
But Westminster Abbey argued refusing to lower its flag would not have helped the "desperately oppressed Christian communities of the Middle East".
"For us not to fly at half-mast would be to make a noticeably aggressive comment on the death of the king of a country to which the UK is allied in the fight against Islamic terrorism," a spokesman said.
The Archbishop of Canterbury, The Most Rev Justin Welby, told Sky News: 'Freedom of religion is essential and freedom to express Christian faith in Saudi Arabia is something that should happen.
"A few weeks ago there was a group of migrant workers arrested for holding a private service in a flat. That's not right.
"But I know that King Abdullah himself - it's a complicated place Saudi Arabia, like all countries - King Abdullah himself is someone who has worked very very hard on these issues and has contributed much and I think it's right that the prime minister should send condolences and should recognise what he's done over the years."
King Abdullah had run the country as de facto leader since the mid-1990s after his predecessor King Fahd suffered a debilitating stroke.
He was admitted to hospital on 31 December suffering pneumonia and the royal court announced that he was breathing with the aid of a tube.
He has been succeeded by his 79-year-old half-brother, Salman.