Police raided the office of Sri Lanka's defeated presidential candidate Sarath Fonseka and arrested 15 of his staff Friday, after officials accused the former army chief of plotting to overthrow the government and assassinate his victorious rival.

Fonseka called the allegations fabricated and vowed to push on with his political career by challenging President Mahinda Rajapaksa's party in upcoming parliamentary elections.

The two men were close allies when they crushed the Tamil Tiger rebels last year, but fell out after the war ended in May. Fonseka joined the opposition to run against the president, with both sides campaigning on their record as heroes who ended the 25-year separatist rebellion.

Rajapaksa swept to a resounding victory in Tuesday's vote, beating the former army chief by 17 percentage points. However, Fonseka rejected the results and accused the government of stealing more than a million of his votes during the tallying process.

The government denied this, and in turn accused Fonseka of plotting to kill Rajapaksa and overthrow the government with the help of army deserters and former military officers.

Dozens of policemen raided Fonseka's office in Colombo on Friday, taking away computers and detaining 15 ex-military personnel who worked there, said Shiral Laktilaka, Fonseka's lawyer.

A government spokesman confirmed the raid, but did not give other details.

The former army chief was at his house elsewhere in the capital at the time of the operation, said Mano Ganeshan, an opposition official.

Police said they were looking for explosives during their five-hour long search of the building, said an office worker, who spoke on condition of anonymity for fear of retaliation from authorities.

"This is the price we pay for democracy because he decided to contest the election," Laktilaka said.

Following his defeat, Fonseka said the government was harassing his associates, and had recalled his 80-strong state-provided security force, a move he says put his life in danger.

He also said authorities put his name on the list of people who cannot leave the country, a charge denied by the government.

The acrimonious post-poll fallout between the one-time allies will likely continue until the general elections. Fonseka announced that he plans to run for a parliamentary seat.

The president can dissolve parliament and call the general elections at any point between now and April, when its six-year mandate expires. Rajapaksa and his coalition partners hold a majority in parliament.

Meanwhile, detectives questioned an editor of a pro-opposition newspaper, said opposition lawmaker Vijitha Herath.

Chandana Sirimalwatte of the Lanka newspaper was asked to report to the Criminal Investigations Department on Friday, Herath said, adding that officials were preparing to obtain an order from the government that can allow for a 90-day detention under the country's wartime emergency laws.

Herath said he did not know why the editor was summoned for questioning. The newspaper backed Fonseka in the election and has reported on alleged government corruption.

Separately, authorities ordered a Swiss radio journalist to leave Sri Lanka by Monday, after she asked critical questions at a post-election news conference earlier in the week, said Andreas Notter, a spokesman for the national broadcaster.

Notter said Friday that the government in Colombo gave no reason for the expulsion of their South Asia correspondent Karin Wenger.

Officials at Sri Lanka's diplomatic missions in Geneva and Berlin couldn't be reached for comment.

Sri Lanka has in the past expelled journalists, U.N. officials and aid workers who have spoken publicly about the plight of civilians during the country's civil war and political repression.