LONDON, United Kingdom- Rishi Sunak on Tuesday became Britain's third prime minister this year and the first person of colour to lead the former imperial power, vowing to overcome an economic crisis provoked by the "mistakes" of Liz Truss's calamitous 49-day tenure.

In his first order of business, Sunak retained Jeremy Hunt as chancellor of the exchequer, bidding to keep financial markets on side after Truss's budget plans shocked investors, and also retained her foreign and defence ministers, among others.

Sunak, a practising Hindu who at 42 is Britain's youngest leader since 1812, became the ruling Conservatives' new leader on Monday after a prior stint as chancellor himself.

Addressing the nation in Downing Street Tuesday shortly after his appointment by King Charles III, Sunak said the country faced "profound economic crisis".

"I will place economic stability and confidence at the heart of this government's agenda," Sunak vowed, capping the latest extraordinary twist in UK politics following Boris Johnson's demise in July.

- 'Mistakes' -
Truss -- chosen by Tory members over Sunak in the summer to replace Johnson -- left office as the UK's shortest-serving premier in history.

The 47-year-old wished the new leader "every success", noting she remained "more convinced than ever" that Britain needs to be "bold" in confronting the challenges it faces.

Sunak countered that, though Truss was motivated by a well-intentioned desire to kick-start growth, her tax-cutting measures were "mistakes nonetheless".

"And I have been elected as leader of my party and your prime minister in part to fix them," he said.

"The government I lead will not leave the next generation... with a debt to settle that we were too weak to pay ourselves," he added, helping to drive the pound more than one percent higher against the dollar.

Sunak, a wealthy descendant of immigrants from India and East Africa, secured the top job after rival contender Penny Mordaunt failed to garner enough nominations from Tory MPs and Johnson dramatically aborted a comeback attempt.

Breaking his silence, Johnson offered his "full and wholehearted support" to Sunak -- having privately blamed his ex-minister for toppling him in July.

Sunak in turn praised Johnson, but in a nod to the many scandals that brought Johnson down, vowed his own premiership would offer "integrity, professionalism and accountability at every level".

- Cabinet continuity -
In some of the other cabinet retentions aimed at stability, Sunak kept James Cleverly as foreign secretary, Ben Wallace in the defence brief and Kemi Badenoch in international trade.

Just days after she left Truss's cabinet, hardline right-winger Suella Braverman was re-appointed as interior minister, in charge of policing and immigration control.

Grant Shapps, who had briefly replaced Braverman, was named business secretary with partial oversight of climate policy, instead of Johnson loyalist Jacob Rees-Mogg.

Sunak brought close ally Dominic Raab back as deputy prime minister and justice secretary, and veteran cabinet member Michael Gove to tackle the country's entrenched regional inequality.

Mordaunt remains in a post overseeing government business in parliament, which may disappoint the ambitious centrist who had been tipped for a more senior role.

The line-up "reflects a unified party and a cabinet with significant experience, ensuring that at this uncertain time there is continuity at the heart of government," a Downing Street source said.

The new top team is set to meet early Wednesday, British media said, before Sunak faces his first weekly face-off with opposition parties at "Prime Minister's Questions" in parliament.

- Foreign calls -
In his first call with a foreign leader, Sunak told Ukrainian President Volodymyr Zelensky Britain would continue its "steadfast support" following Russia's invasion.

He also spoke to US President Joe Biden, who had earlier hailed his appointment as the first British-Indian prime minister as "groundbreaking" and "pretty outstanding".

"President Biden said that the UK remains America's closest ally, and the Prime Minister agreed on the huge strength of the relationship," a Downing Street spokeswoman said.

European leaders offered their own congratulations, while Irish premier Micheal Martin reminded Sunak of their "shared responsibility" to safeguard peace in Northern Ireland following tensions under Johnson and Truss.

Domestically, Labour leader Keir Starmer praised Sunak on "making history as the first British-Asian PM".

But he reiterated accusation the Tories "have crashed the economy" and that the public needs "a say on Britain's future".

Sunak has rebuffed opposition calls for a snap general election after becoming the latest leader who lacks a direct mandate from the electorate.

Pollster Ipsos said that 62 percent of British voters want an election by the end of the year.

Voters in London Tuesday spelled out the scale of his challenge.

"The whole country is in shambles at the moment, he has got to make a difference, if he doesn't there's going to be riots," insurance adviser Helen Gorman told AFP.