Motorola has named an alleged spy as a co-defendant in a lawsuit against Chinese telecoms group Huawei over the alleged theft of trade secrets.

In the civil lawsuit, Motorola alleged that Huawei had knowingly taken trade secrets from a company employing a dozen former employees of the US group, including Jin Hanjuan, who faces criminal charges of economic espionage in the US.

The civil case comes at a sensitive time for Huawei, which has expanded rapidly to become one of the world's largest telecom equipment suppliers. It already faces fierce opposition in the US and other countries because of suspected ties to the Chinese military, which the company consistently denies.

In an amended lawsuit filed last week in a Chicago court, Motorola alleges Huawei and its founder Ren Zhengfei, a former officer in the People's Liberation Army, began working with Chinese-born Motorola employees as early as 2001.

In the lawsuit, the company accuses a dozen former employees of setting up Lemko, a rival company, in 2002 while they were still employed by Motorola, and stealing trade secrets over the next five years, some of which they allegedly transferred to Huawei. Motorola claimed Ms Jin was secretly employed by Lemko in 2005 while still an employee at Motorola. Her criminal indictment alleges Ms Jin obtained Motorola trade secrets that “would benefit a foreign government, namely the People's Republic of China, specifically its military”.

According to an affidavit from the US Federal Bureau of Investigation, Ms Jin was caught at O'Hara airport, Chicago, in 2007 carrying Chinese military catalogues and stolen Motorola technology. Her criminal indictment alleged that she was also employed around the same time by a company referred to only as “Company B”, which was based in China and “contributed to the Chinese national defence and developed telecom technology and products for the Chinese military”.

Her indictment also alleges that she was introduced to “Company B” and its representatives by Pan Shaowei, a former Motorola employee and chief technology officer of Lemko.

Motorola has alleged in the lawsuit that he was the main interface between Lemko and Huawei and transferred trade secrets to the Chinese company. The US Attorney's Office in Chicago which is prosecuting the case has refused to identify “Company B”.

Huawei refused to comment on the criminal case but issued a statement saying Motorola's complaint was “groundless and utterly without merit” and it would “vigorously defend itself against baseless allegations”.

Lemko said: “We believe Motorola initiated this litigation against Lemko and its employees to financially weaken the company.”