Two Chinese American scientists who were indicted by the United States for spying only to see their charges abruptly abandoned spoke out Tuesday against the ordeal they had been put through.

The cases have led some US lawmakers and Chinese American community groups to demand a probe into whether they were unfairly targeted because of their background.

Professor Xiaoxing Xi, former chair of physics at Temple University, learned last week he would not be charged with spying for sharing a schematic with a Chinese colleague.

In March, another naturalized US citizen, government hydrologist Sherry Chen, discovered she would not be tried for accessing sensitive data and lying to federal agents.

In both cases, their lawyer said, Department of Justice prosecutors dropped the criminal cases against them once confronted with detailed explanations of the facts.

Neither face further criminal prosecution, but Chen remains distraught at losing the job she loved working at the US National Weather Service on a model to predict river flows.

On Tuesday, they spoke of the pain their arrests brought their families -- and their supporters demanded government act to prevent such mistakes from happening again.

Sherry Chen had been in America for two decades and an exemplary Weather Service employee building a detailed model of water flows in US rivers for eight years.

She saw her work as protecting US lives and property from flood and was left shattered after she was accused of crimes that could have seen her spend 25 years in jail.

Chen was arrested last year, aged 59, at her office in Wilmington, Ohio -- handcuffed in front of her colleagues a few days before the start of the US holiday season.

"I love Christmas lights," she told reporters, her voice cracking and her eyes swelling with tears after she and her husband drove eight hours to Washington to tell her story.

"I really, really enjoy the Christmas season, but not last year," she said, describing how television vans pulled up outside her house after news of the case broke.

"The few times I ventured outside of my house to get some fresh air, I tried very hard not to look at those lights. Those decorations were not as beautiful as I remembered."

Xi also grew emotional as he told of how in May federal agents came to his home, handcuffed him and led him away in front of his uncomprehending wife and daughters.

"I don't think my wife has had a single night of good sleep since that day," he said, pausing and blinking back tears.

Xi spoke of the guilt he feels at what his family went through -- he had to cancel a plan to visit his 90-year-old mother in China -- despite his innocence.

- 'Innocent clients' -

Both scientists thanked their lawyers and the Chinese American community for standing by them while their legal team and supportive colleagues responded to the charges.

Defense counsel Peter Zeidenberg, of Washington law firm Arent Fox, deflected their praise, saying: "It's always easy to be a great lawyer when you have innocent clients."

Supporters such as Jeremy Wu and Haipei Shue of Chinese American community groups the Committee of 100 and United Chinese Communities compared the case to that of Wen Ho Lee.

Lee, who worked at the Los Alamos nuclear laboratory, was charged in 1999 with spying for China and was held in solitary for nine months before the case collapsed.

These cases and two others have convinced some in Washington that the FBI, amid concern over Chinese espionage, has been careless or prejudiced in targeting innocent US citizens.

"We now have another example of apparent discriminatory arrest and discriminatory charging by federal officials," said Representative Ted Lieu, a California Democrat.

The Congressional Asian Pacific American Caucus echoed calls for an inquiry, and Representative Grace Meng of Queens, New York, lambasted apparent shortcomings in the FBI probe.

"The government need to be held accountable to being fair, and must respect the civil rights of all Americans, regardless of race," she said.

Meanwhile, now cleared, Chen is preparing to challenge her dismissal from the National Weather Service.