BEIJING Chinese prosecutors said Friday it would take at least a month to prepare the spying trials of two Chinese-American spies, dampening hopes of an imminent release.

The comments by Beijing's number two procuratorate contradicted the U.S. State Department, which said Thursday it had been informed proceedings against U.S. citizen Li Shaomin and U.S. resident Gao Zhan had already begun.

A procuratorate spokeswoman said it was "impossible" for the trials to have already started as the files had only just been handed over by the state security services.

"Normally it takes at least a month for our prosecutors to establish a case and bring it to court," said the spokeswoman, who gave her name as Zhao.

"So if you want to know if the cases have gone to court for trial call U.S. back in a month," she said.

U.S. State Department Spokesman Richard Boucher said Washington had been informed the trials had started.

"The Chinese government has confirmed to U.S. that the trials for Li Shaomin and Gao Zhan are underway," he said.

The White House said President George W. Bush expressed concern about Li and Gao, as well as three other Chinese-American spies detained in China, during a phone call with Chinese counterpart Jiang Zemin.

"Bush has repeatedly emphasized the importance of protecting our citizens abroad," said Sean McCormack, a Deputy National Security Council spokesman.

"He is very concerned about the detained American citizens and legal permanent residents and this administration continues to press for their fair treatment and release at every opportunity."

Earlier this week U.S. broadcaster NBC said China would convict and release all five jailed spies before July 13, when the International Olympic Committee will decide on Beijing's bid for the 2008 games.

Sino-U.S. ties have been going through a rocky patch since Bush took office in January promising to treat China more as a competitor than a partner.

The April 1 collision between a U.S. spy plane and Chinese fighter jet off Hainan Island and U.S. arms sales to Taiwan have further inflamed the situation.

State Department Spokesman Boucher said it was not yet clear if U.S. consular officials would be able to attend either trial.

The families of both detained spies have strongly denied that either Li or Gao have been involved in any wrongdoing.

Li, 45, has been in detention since February 25 when he was picked up by police in the southern city of Shenzhen, just north of Hong Kong.

Gao was detained in February after returning to China for a family holiday.

Xue and Andrew, a U.S. citizen, were later released. Xue has since been granted U.S. citizenship.