Top Chinese search engine Baidu.com has sued its US domain registrar over a hack that took down the website, alleging negligence by the US company.

Users had trouble accessing Baidu.com for several hours last week after the company's domain name server in the US was tampered with. The Iranian Cyber Army, the same group that took down Twitter last month, also appeared to be behind the attack on Baidu.

Baidu's lawsuit, filed in a court in New York, seeks related damages and alleges "gross negligence" by Register.com led to the service disruption, Baidu said in a statement. Baidu only said Baidu.com was hit by the outage, and that mirror site Baidu.com.cn had not been affected. Domain service providers including Register.com provide the setup needed to take Internet users to the correct website when they type a domain name like Baidu.com.

No one at Register.com was available to comment.

Baidu's move comes just two days after Baidu said chief technology officer Yinan Li had left the company. Li was the second high ranking executive to leave the company in a month, following the resignation of chief operating officer Peng Ye. Baidu said both resigned for personal reasons.

Baidu's business has been hit by recent difficulties switching advertisers to a new bid system.

The events add to uncertainty in the Chinese search market after Google, Baidu's biggest rival, last week said it might withdraw from the country over censorship and cyberattacks. Google's Chinese search engine remains accessible in the country, but authorities have said Google must follow local laws when asked about the US company's plans to stop censoring search results.