Komorowski sworn in as Polish president

WARSAW (Reuters) - Bronislaw Komorowski took the oath of office as Poland's new president on Friday and vowed to build national unity, but the man he beat for the top job boycotted the ceremony in a sign of enduring political tension.

Komorowski, a moderate conservative from the ruling Civic Platform (PO), defeated Jaroslaw Kaczynski in the July 4 run-off of an election triggered by the death of Kaczynski's twin brother, President Lech Kaczynski, in a plane crash in April.

"Poland needs cooperation between the most important institutions of the state, between the government, the parliament, the president but also between political parties, between those in government and those in opposition," Komorowski said in a speech to parliament after taking the oath.

"As president I declare my will for such cooperation."

Jaroslaw Kaczynski, who leads the right-wing main opposition Law and Justice (PiS), and some of his deputies stayed away from the ceremony. Lech Kaczynski, a combative right-winger, and the centrist government of Prime Minister Donald Tusk were often at loggerheads as the president vetoed some draft legislation.

Asked why Kaczynski did not attend Friday's ceremony, the deputy head of the PiS parliamentary party, Beata Szydlo, told Reuters: "Clearly he has some other things to do."

Komorowski reached out to his opponent in his speech.

"I want to thank the nearly 9 million Poles who brought me to this post. But I also remember that nearly 8 million Poles voted for my rival and I aim to perform my duties hoping to convince and satisfy these Poles as well," Komorowski said.

WORKING WITH GOVT

The mustachioed, gently-spoken Komorowski, a Tusk ally, is expected to work much more smoothly with the government as it tries to tackle Poland's growing debt pile and large budget deficit without derailing a still-fragile economic recovery.

In his speech, Komorowski paid tribute to the 96 people who died in the April 10 plane crash in Russia. But he said Polish democracy had proven resilient in dealing with the tragedy, which claimed the lives of top officials along with Lech Kaczynski and his wife.

Komorowski stressed Poland's commitment to the European Union, which it joined in 2004, and said his first overseas trips as president would be to Brussels, Paris and Berlin. He also vowed to back the recent Polish-Russian rapprochement.

In a rare picture of national reconciliation, Komorowski posed for the cameras with former presidents and prime ministers from both left and right, including the ex-leader of the Solidarity trade union that toppled communism in 1989, Lech Walesa, and Poland's last communist leader, Wojciech Jaruzelski.

Kaczynski's no-show at Friday's ceremony also drew criticism from Jerzy Buzek, a former center-right prime minister who heads the European Parliament.

"There are certain events in a democratic state when all should be present and when their absence is regarded as a deliberate protest," Buzek said.

Earlier this week, supporters of the Kaczynski twins blocked an attempt by the authorities to move a large wooden cross, erected shortly after the crash, from in front of the presidential palace to a nearby church.

The noisy protests and clashes with police underscored the strong emotions still felt by some Poles about the tragedy.

Komorowski, 58, is Poland's fourth post-communist president. A historian by training, he was born in communist Poland into a family with aristocratic roots. He and his wife Anna have five grown-up children.

A member of underground pro-democracy organizations under communism, he later served as defense minister in 2000-01 and became speaker of the lower house of parliament, the Sejm, in 2007 when Tusk's PO won the parliamentary election.

(Writing by Gareth Jones, editing by Philippa Fletcher)