As Taliban captured key customs posts bleeding the administration of revenue, reinforcing the government’s isolation as the militants make swift gains, Afghanistan’s acting finance minister Khalid Payenda has resigned and left the country

Payenda has “resigned and left the country because Afghanistan is grappling with declining revenues after the takeover of the custom posts,” Finance Ministry spokesman Mohammad Rafi Tabe said in a phone interview Wednesday. “The deteriorating security situation” and traveling to be with his ailing wife abroad, were the other reasons Tabe gave.

It wasn’t immediately clear where Payenda was going to.

The former minister tweeted Tuesday to say he was quitting his post but gave no reasons for it. The deputy minister for customs and revenues, Alem Shah Ibrahimi, will be in charge until a new appointment is announced.

Payenda wasn’t immediately available for comment.

With U.S. and NATO troops slated for a complete exit by Aug. 31, a resurgent Taliban have overrun several provincial capitals in recent days. The militants have also seized several crucial custom posts causing President Ashraf Ghani’s government to lose as much as $30 million in import duties last month alone. The taxes account for about half of Afghanistan’s total domestic revenues, estimated to be about 216.5 billion Afghanis this year.