LONDON -- British Prime Minister Tony Blair, who has been under increasing political pressure because of the war in Iraq, was admitted to a hospital Sunday after suffering an irregular heartbeat, but was released after several hours of treatment, his office said.

Blair, 50, was taken to London's Hammersmith hospital, treated and released after five hours, his office said. The prime minister was feeling "fine" after returning home, his office at No. 10 Downing Street said in a statement.

"This was completely successful. He was in hospital for four to five hours and is now back at Number 10. The hospital says this is a relatively common condition and is easily treated," it said.

"He has suffered no damage and he is fine. There is no reason why this should reoccur. They have advised him to rest for 24 hours."

Blair was expected to return to work full-time on Tuesday, his office said.

Blair, who has been in office for 6 1/2 years, returned Friday from a European Union summit meeting. This was the first hint of any health problems for Blair since he took power.

This year has been the most stressful for Blair since becoming prime minister. He has faced a storm of criticism across Britain for his decision to commit British troops to military action in Iraq earlier this year.

Blair also has appeared increasingly tired in public, often looking haggard at press conferences and other forums where he has faced constant criticism from a hostile media. He also has fended off discontent inside his Labor Party, whose left wing is unhappy about his centrist policies.

Since the war, his government has been on the defensive because coalition forces have not found evidence of weapons of mass destruction -- the heart of Blair's case for military action to oust Saddam Hussein.

Two of Blair's Cabinet ministers resigned to protest the invasion, and public opinion polls have charted growing disillusionment with his government.

There was further strain when the government became embroiled in a bitter feud with the British Broadcasting Corp. over a news report quoting an unidentified scientist as saying the government "sexed up" a dossier of evidence about Iraqi weapons.

The source, weapons adviser David Kelly, was found dead July 18 of an apparent suicide. Blair was called to give testimony at a judicial inquiry into Kelly's death.

The BBC and other television and radio channels interrupted their normal programs to report that Blair had been admitted to hospital.

Blair has always appeared young and vigorous and there have rarely been hints of any health problems since he took power, apart from occasional colds.

At international conferences, Blair is noted for appearing much younger than many of his fellow government leaders.

But the prime minister is known for taking a very direct role in all the main aspects of his government and often carries a punishing workload.

If the prime minister were temporarily incapacitated, Deputy Prime Minister John Prescott would take on his duties, Blair's office said.

If he were unable to continue in office, the governing Labor Party would have to elect a new leader, who would then become prime minister.