Ma mentioned the poll results during a meeting of the Kuomintang's Central Standing Committee in Ilan County open to the media. Television stations bleeped out Ma's words as if he were uttering an obscenity.

The Ilan Election Commission said yesterday it would write a letter to the suspect and request an interview with him. If found guilty, he would be fined between NT$500,000 to NT$5 million, regardless of his position in society, a commission spokesman said. The investigation would likely only come to a conclusion after the elections, he added.

The post of Ilan County Magistrate is one of the most hard-fought political offices in the Dec. 5 elections as first-term KMT incumbent Lu Kuo-hua is fighting a difficult battle against Lin Tsung-hsien, the candidate for the opposition Democratic Progressive Party. Lu was the first KMT candidate in 28 years to win the county in 2005.

"When he was speaking, the president did not realize he might be violating the Election and Recall Act. He felt deeply uncomfortable and thought he needed to express an apology to society," KMT Secretary-General Chan Chuen-po told a news conference yesterday.

DPP Chairwoman Tsai Ing-wen demanded the Central Election Commission fine him. She also described the incident as a side effect of Ma combining the jobs of head of state with ruling party chairman.

A president who controls so many administrative resources should not be so absent-minded and refrain from using his resources to intervene in the election campaign, she said.

DPP lawmaker Tsai Huang-liang said this case would prove whether the CEC was independent, fair and objective. The opposition said it would ask the top government watchdog body, the Control Yuan, to issue sanctions against the CEC if the latter did not act.

Former Premier Frank Hsieh accused him of illegally influencing the Ilan result.

Outspoken KMT lawmaker Chiu Yi also criticized the president. Ma was a professional politician and lawyer, so he could not say he didn't know, Chiu said, adding his voice to the calls for an apology.

The opinion poll controversy was the third incident surrounding Ma's behavior on the campaign trail this week.

On Tuesday, police and KMT supporters clashed with the entourage of former Premier Frank Hsieh as both Ma and Hsieh were walking around with their candidates in Hsinfeng, Hsinchu County. The DPP rejected claims by the police that security for the president needed to be tight and that the opposition should have applied for permission for its event.

Later, the DPP presented evidence that about 20 of the apparent KMT supporters in Hsinfeng were actually members of Ma's official security detail wearing ruling party campaign jackets.

The National Security Bureau, Taiwan's top intelligence agency, apologized for the incident Wednesday and promised disciplinary action against those responsible.

The county election campaign has also been marred by numerous allegations of vote buying, with several KMT candidates and campaign officials being detained or investigated.