South Korean prosecutors said Tuesday they had arrested five local Internet company chiefs for violating copyright laws, as one of the firms claimed the move was politically motivated.

The presidents of Nowcom and four other online service providers were arrested Monday for illegally spreading movie files online, according to the office of the Seoul central district prosecutor.

They were charged with having paid "uploaders" for illegally posting copyright film files or video clips on their websites, the office said.

Nowcom said it suspected the arrest of its chief was politically motivated to suppress online anti-government campaigns.

Nowcom runs video-sharing website Afreeca.com, where more than seven million people have watched real-time broadcasts of candlelit vigils against President Lee Myung-Bak.

"We cannot but suspect that the government was politically motivated to stop the spread of the candlelit vigils with the investigation," Nowcom said in a statement on its website.

In the past months tens of thousands have taken to the streets to denounce Lee's decision to resume US beef imports amid mad cow disease fears.

The prosecution denied Nowcom's claims.

"The investigation had nothing to do with candlelit vigils as it was launched in April, long before the protests started," an unnamed prosecutor told Yonhap news agency.

Prosecutors also said Afreeca.com is not the target of their probe.