MANILA - President Rodrigo Duterte has ordered an investigation into the alleged anomalies surrounding state-run Philippine Health Insurance Corporation (PhilHealth), Malacañang said Friday after an officer resigned, claiming widespread corruption in the firm.

Duterte tasked his special assistant Undersecretary Melchor Quitain to conduct the investigation, Presidential Spokesperson Harry Roque said.

The investigation order came after PhilHealth anti-fraud officer lawyer Thorrsson Montes Keith said he was resigning because the mandatory payment of PhilHealth contributions by overseas Filipino workers was unconstitutional, and due to an alleged unfair job promotion process.

"We view the allegations of Mr. Keith a serious matter and therefore enjoin him, and other officials, to cooperate with the ongoing investigation," Roque said.

• PhilHealth officer resigns due to 'widespread corruption' in agency

PhilHealth President Ricardo Morales, however, said the resigning employee was only "vengeful" after being denied for a certain post.

"Baka ito iyong ganti niya. Parang vengeful, spiteful siya dahil tinanggihan ko siya noon," Morales told ABS-CBN's TeleRadyo.

(Perhaps this is his revenge. He appears vengeful, spiteful because I refused him before.)

• PhilHealth chief says employee accusing him of corruption unqualified, vengeful

The fresh allegations are the latest in a string of corruption issues surrounding the state health insurance firm.

In June, Roque said Morales "failed" to clean up corruption in PhilHealth as he alleged that there are still crooks within the state health insurance firm.

• PhilHealth chief belies corruption 'syndicate,' billions of missing funds

Morales, however, denied any large-scale effort to defraud PhilHealth but admitted "inefficiencies" in the processing of claims within the state health insurance firm.