Zhang Hao, a professor at Tianjin University who had been detained in the US on accusations of economic espionage in May, has been released on a $500,000 bond, a press official from the university said on Thursday.

Zhang is one of six Chinese nationals charged by the US government with economic espionage. US authorities said the accused stole wireless semiconductor technology from Avago Technologies and Skyworks Solutions and passed it on to Chinese universities and companies. The technology was used in military systems, prosecutors said.

US Magistrate Judge Nathanael Cousins in San Jose, California, had ordered Zhang freed on a $500,000 bond on July 8. The bond is secured by $225,000 in US-based retirement savings and other financial assets belonging to Zhang and his wife, as well as equity in four Tampa, Florida, homes owned by Li Jiang, whose nephew is married to Zhang's sister. The assets are worth nearly $625,000, Zhang's attorney Thomas Nolan said.

"It is unbelievable that US authorities detained the professor again after the court ordered the release and used various means to prevent the meeting between Zhang and the judge," an anonymous source said to have knowledge of the case told the Global Times, a publication in China.

The source said that Zhang is in good physical condition and will stay at a friend's house in a court-approved arrangement but will not be allowed to leave Northern California.

Zhang, who founded a chipmaking firm in Tianjin in 2011, was arrested at Los Angeles International Airport on May 16 en route to an international microwave conference.

He has been "maliciously and falsely accused" by US authorities, his wife Fan Liping wrote in a June 3 letter posted on social media. She described the professor as a simple man who pursued research.

In the letter, Fan seeks donations, saying the family needs between 20 million yuan ($3.22 million) and 35 million yuan in legal fees.

Experts have said that Zhang's release indicates a softening of the US stance and could ease some tensions between the two powers ahead of President Xi Jinping's state visit in September.

Foreign Ministry spokesman Hong Lei has denied that Chinese government-backed companies were carrying out industrial espionage. He called for the US to stop the "irresponsible and groundless accusations" and help boost Sino-US ties.

"US politicians are good at taking the neutral course - avoiding angering voters in favor or against China," said Wang Hongwei, a national security professor at Renmin University.

Reuters contributed to this story.

(China Daily USA 07/31/2015 page1)