SEOUL - Two former heads of South Korea's spy agency were arrested Friday on suspicion of paying millions of dollars in bribes to aides of ousted president Park Geun-Hye, as a widening corruption scandal rocks the country.

Nam Jae-Joon and Lee Byung-Kee, ex-heads of the National Intelligence Service (NIS), were arrested for allegedly handing at least 4 billion won ($3.63 million) of their agency's budget to Park's aides in monthly payments in exchange for career advancement.

The Seoul Central District Court approved the arrest warrants on the two, citing risk of flight and destruction of evidence.

Former South Korean leader Park was toppled this year and is in custody while on trial for graft and influence-peddling.

Nam and Lee, who respectively served under Park from 2013 to 2015, face charges including embezzlement, bribery and causing losses to state coffers.

The pair reportedly told prosecutors that they had offered the "monthly payment" to Park's office at the personal request of her key aides.

Two former aides to Park were arrested earlier this month on suspicion of taking the money from the NIS, and reportedly told investigators they had done so on the president's order.

South Korea's spy agency has already been accused of abusing its power to meddle in politics under two conservative ex-presidents.

A former senior NIS official was detained last month for allegedly leading a string of operations to monitor and undermine high-profile figures and celebrities critical of Park and her predecessor.

Ex-spy chief Won Sei-Hoon was jailed for three years in August for ordering NIS officials to mount an online smear campaign against Park's key rival in the 2012 presidential election.

The closely-fought election saw Park defeat left-leaning Moon Jae-In.

Moon was elected earlier this year after Park's impeachment over the corruption scandal that also implicated the country's top business group, Samsung.

Park is accused of offering policy favours to business tycoons who helped enrich her secret confidante, Choi Soon-Sil, as well as allowing her friend - who had no title or security clearance - handle state affairs, including senior nominations.

Choi is in also in custody while on trial for bribery and abuse of power.

Samsung heir Lee Jae-Yong is in jail, appealing against his five-year prison term over bribery and perjury.