Afghan Defense Minister Abdul Rahim Wardak resigned on Tuesday, August 7 after losing a no-confidence vote in parliament, leaving President Hamid Karzai scrambling to find a replacement for one of his top security tsars as insurgent attacks mount, Reuters said.

Wardak, in charge of the army and one of the country's two key security ministers, told reporters he accepted parliament's decision, which has clouded NATO plans to hand security responsibilities to Afghan forces before the end of 2014.

Karzai's increasingly unpopular government was already under a cloud, with Finance Minister Hazarat Omar Zakhilwal vulnerable as a result of accusations aired on Afghan television that he stashed more than $1 million in overseas banks.

The fractious parliament voted on Saturday to remove Wardak and Interior Minister Bismillah Mohammadi after recent insurgent assassinations of senior officials, as well as cross-border attacks blamed on Pakistan.

While Karzai opted to keep him in place in an acting role to underpin stability, Wardak's decision to quit immediately leaves one of his most vital Cabinet posts vacant at the peak of the summer fighting months and as U.S. and French troops draw down.

It was not immediately clear how soon Karzai would be able to replace the veteran four-star general and ethnic Pashtun from eastern Wardak province, who is credited by Western diplomats with helping forge the fledgling Afghan National Army into an increasingly effective force against insurgents.

Karzai faced constraints in finding a replacement who could maintain ethnic harmony in his inner circle, while also needing to win over lawmakers whose backing he needs to deliver a corruption crackdown promised to Western donors.