London, May 12 (DPA) Conservative leader David Cameron became Britain's new prime minister Tuesday after forming an historic coalition government with Liberal Democrat Nick Clegg as his deputy.

The new Conservative-Liberal alliance, resulting from last week's general election, is Britain's first coalition government since World War II.

Britain's new Con-Lib era ends 13 years of Labour rule, which began with by ex-prime minister Tony Blair's 1997 landslide victory.

US President Barack Obama and German Chancellor Angela Merkel were among the first world leaders to congratulate Cameron, who at 43 is Britain's youngest prime minister in 200 years.

Downing Street said Obama invited Cameron to visit the US in July and was looking forward to seeing him before then at international summits.

Cameron received a congratulatory call and an invitation to visit Berlin "at the earliest possible opportunity" from Merkel, who is known to be critical of the Conservatives' traditional scepticism on Europe.

However, analysts in London said Clegg's leading role in the new British coalition government was likely to help ease British tensions with fellow EU members.

"Compared with a decade ago, this country is more open at home and more compassionate abroad," Cameron said.

It was confirmed late Tuesday that Clegg, also 43, would be deputy prime minister in the new administration, while veteran Euro-sceptic William Hague will become foreign secretary.

Long-term Cameron ally George Osborne would become Chancellor of the Exchequer, where Liberal economic spokesman Vince Cable was likely to become his number two as chief secretary to the treasury.

The defence portfolio was expected to go to Conservative Liam Fox. Unconfirmed reports said the Liberals would have a total of four Cabinet posts.

"I aim to form a proper and full coalition government with the Liberal Democrats," Cameron announced on the steps of Downing Street, following days of tough negotiations.

"We have some deep and pressing problems - a huge deficit, deep social problems, a political system in need of reform. But I believe together we can provide that strong and stable government that our country needs."

Clegg, speaking after the coalition deal had been approved by his party's executive and parliamentarians, said he hoped for a "new kind of government".

Although the Conservatives and Liberals were "different political parties", he hoped that they could overcome their differences "to deliver good government for the good of the whole country".

Clegg was determined to prove that "new politics were not just possible but also better", he said.

Cameron, along with his pregnant wife, Samantha, had earlier visited Buckingham Palace for his appointment as prime minister by Queen Elizabeth II.

In a series of fast-moving events late Tuesday, Labour's Gordon Brown resigned after nearly three years as prime minister.

He conceded defeat in the election after he had failed to persuade the Liberals to form a government with Labour.

"I loved the job, not for its prestige, its titles and its ceremony, which I do not love at all," Brown said in his resignation speech outside Downing Street.

He said he would now return to his "first job in life," being a "husband and a father."

Brown's wife, Sarah, stood by his side with their two young sons for a photocall and Brown's last official trip to Buckingham Palace.

The traditional change-of-power ceremony followed five days of political high drama, resulting from the inconclusive May 6 general election, which gave neither of the two big parties an outright majority.

As a result, Clegg, the new "kingmaker" of British politics, had offered both sides talks about a new government.