BANGKOK - A bomb exploded at a bus stop in central Bangkok on Sunday, killing one person and wounding 10 in an attack that reignited tensions two months after the end of deadly opposition protests.

The explosion came hours after polls closed in a closely watched by-election in the capital, with initial results suggesting a leader of the "Red Shirt" anti-government movement had lost to a member of the elite-backed ruling party.

The bomb went off in the early evening at a bus stop in front of a supermarket in the same central shopping district occupied by the Red Shirts during their two-month-long mass rally, which ended with an army crackdown in May.

"It was an attempt to injure innocent people," said government spokesman Panitan Wattanayagorn.

"The authorities will have to increase preventative measures," he added, without elaborating.

The victim was a 51-year-old man who died in hospital, an official at the Erawan emergency centre told AFP.

The scene of the attack was sealed off by police and forensic experts were seen collecting wires and small batteries at the site.

The blast appeared to have been caused by a small time bomb "designed to create fear," a soldier at the scene told AFP.

The explosion shattered an uneasy calm that had returned to the capital since the military crushed the Red Shirts' two-month-long mass protests with an assault on their sprawling encampment in the heart of the capital.

Thai society remains deeply divided following the political violence, in which 90 people died and about 1,900 were injured in a series of street clashes between armed troops and demonstrators.

After the crackdown, enraged demonstrators torched major buildings around the capital, including a major shopping mall near the scene of Sunday's blast.

About one fifth of the country, including Bangkok, remains under a state of emergency which bans public gatherings of more than five people and gives security forces the right to detain suspects for 30 days without charge.

The protests by the Reds -- many of whom back fugitive ex-premier Thaksin Shinawatra -- attracted up to 100,000 people demanding immediate elections, but most of the leaders are now behind bars.

They include a top Red Shirt who ran in a by-election in a suburb of the capital Sunday that was seen by many as a referendum on the authorities' handling of the political crisis.

Kokaew Pikulthong, who is in prison on terrorism charges and was not allowed out to campaign, appeared to have lost his bid for a seat in parliament, according to initial results from the Election Commission.

Ruling Democrat Party candidate Panich Vikitsreth looked set to clinch victory with 96,480 votes, ahead of Kokaew of the Puea Thai (For Thais) party on 81,776, the election body said.

Red Shirt lawmaker Jatuporn Prompan said his movement would not give up its struggle to replace Prime Minister Abhisit Vejjajiva's government.

"Puea Thai's fight is not over yet. Puea Thai will keep fighting," Jatuporn said.

The Reds, who hail Thaksin's policies for the poor, view the current government as elitist and undemocratic because it came to power after a court ruling threw out the previous administration.

The vote was considered a litmus test of public opinion as it was the first poll since the Red Shirt protests ended in bloodshed.

The pro-establishment ruling party has traditionally enjoyed solid support in the capital while the Reds' main stronghold is in rural areas, particularly the impoverished northeast.