Former Scottish leader Nicola Sturgeon was on Sunday arrested as part of an investigation into financial irregularities, according to police and UK media.

"A 52-year-old woman has today... been arrested as a suspect in connection with the ongoing investigation into the funding and finances of the Scottish National Party," Police Scotland said in a statement, with British media confirming her identity as Sturgeon.

The woman is in custody and is being questioned by detectives, added police.

It is the third arrest in the probe, which is sending shockwaves through Scotland's political system.

Sturgeon's husband Peter Murrell, the former chief executive of the SNP, was arrested as part of the probe in April.

Murrell has long faced questions over the alleged diversion of £600,000 ($750,000) in SNP donations that were meant to support its drive for Scottish independence.

He also failed to declare a personal loan to the SNP of more than £100,000, which could breach laws on political funding transparency.

He was later released without charge pending further investigation.

Party treasurer Colin Beattie was also arrested in April and later released. 

Sturgeon made her final appearance as First Minister in the Scottish Parliament in March, having announced her intention to retire a month earlier.

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