( AFP ) - Donald Tusk, the leader of Poland's election-winning liberal party, was formally sworn in as prime minister Friday by President Lech Kaczynski.
Tusk and his coalition government's ministers took office in a televised ceremony held at the presidential palace in Warsaw.
"So help me God," said Tusk as he pledged to serve the country, using a formula which, although optional, is traditionally used in government ceremonies in deeply-Catholic Poland.
His 18 ministers were then sworn in one by one.
Tusk, 50, won power after his Civic Platform beat the conservative Law and Justice party in a snap election on October 21.
That brought an end to an unprecedented political double act: defeated prime minister Jaroslaw Kaczynski, 58, is the president's identical twin.
The conservatives had been in power for two years, but Jaroslaw Kaczynski, who became premier in July 2006, had struggled to hold together his fractious three-party coalition.
Tusk has also been forced to form a coalition because Civic Platform missed its goal of obtaining a parliamentary majority, winning 209 of the total 460 seats.
Tusk chose to bring the moderate Polish Peasants' Party, which has 31 MPs, into government, and has made its leader, Waldemar Pawlak, his deputy prime minister.
Law and Justice won 166 seats, and Jaroslaw Kaczynski, who formally stepped down as prime minister on November 5, has become the leader of the opposition.
Tusk has pledged to end the regular tussles with the rest of the European Union, and with neighbouring Germany in particular, which marked Law and Justice's rule.
He also promised to ease tensions with Russia, which have been at their lowest ebb since Poland broke free from the communist bloc in 1989.
He has said he will withdraw Polish troops from Iraq, where 900 soldiers are serving in the US-led coalition; and has warned he will drive a harder bargain in talks with Washington on siting part of a US anti-missile system in Poland.
On the domestic side, he has promised to slash bureaucracy, revive the stalled privatisation process and reform the shambolic health service.
He also wants to spur the already robust economy to try to draw home some of the more than a million Poles who have emigrated since the country joined the EU in 2004.
In addition, he wants Poland to enter the eurozone. The conservatives had regularly expressed scepticism about switching from the national currency, the zloty, to the euro.
Lech Kaczynski, Tusk's longstanding political antagonist who beat him in the 2005 presidential election, still has three years left in office.
The departure of his hardball brother has clipped the president's wings and forced him into a potentially difficult working relationship with Tusk.