One of Kim's aides, surnamed Han, was found to have received 5 million won ($4,634) from a member of Druking's organization in September last year. Han returned the money after Druking's arrest earlier this month.

Investigators are looking into whether any favors were given in return for the money.

Police officials said they sought the warrant to access Kim's phone and bank records to see how frequently the lawmaker communicated with Druking and if any money was transferred between the two.

Police plan to call in Han for questioning on Monday. Officials said they could also consider summoning Kim for questioning depending on the progress of the investigation.

Prosecution officials, meanwhile, bristled at police publicly disclosing the prosecution's rejection of the warrant, saying such information should remain confidential because its disclosure amounts to tipping off the subject of the warrant about what investigators are going to do.

"It's difficult to understand that they made an investigative secret public," a prosecution official said, adding that police should have conducted a supplementary probe to collect additional evidence before requesting a warrant again.

The case was seen as the latest example of tensions between police and the prosecution.

The two law enforcement agencies have been at odds amid police efforts to win greater investigative rights and powers so that they can conduct investigations on their own without the prosecution's oversight. (Yonhap)