The Ministry of Industry and Information Technology will investigate the illegal action of Qihoo 360 and Tencent Inc with other government agencies after China's two Internet giants called a truce in their bitter dispute two weeks ago.

The two firms were asked to cooperate in the probe, the ministry said in a statement over the weekend.

The two companies were also ordered to apologize to the public within five days of the publication of the statement and to ensure proper customer services.

"The illicit action between the two companies has disconnected users with their normal Internet service and caused great inconvenience and dissatisfaction to web users," the statement said.

The ministry ordered them to ensure normal usage of their software and desist from attacking each other.

"We firmly support the lawful right of web users (to choose products), and we want to ensure a healthy market," it added.

On November 10, Tencent said its software QQ is compatible with 360 on computers without the Koukou Guard tool, which Tencent alleged was a "malicious software to QQ," after the weeks-long wrangling.

Beijing-based Qihoo also said in a November 10 statement: "With the intervention by regulators, including the Ministry of Industry and Information Technology, QQ is compatible with 360 now."

Qihoo, which provides the free Internet security tool, claimed in September that Tencent was scanning users' documents through QQ. The dispute escalated on November 3 after Tencent withdrew QQ, the nation's most popular instant messaging tool with more than 1 billion active accounts, from 300 million users of Qihoo's 360 security software. Tencent claimed Qihoo's software damaged the security setup of QQ and threatened the account safety of QQ users.