The U.S. government is urging China to account for all those killed, arrested or still missing from the crackdown on democracy protesters in Tiananmen Square 22 years ago.

State Department spokesman Mark Toner on Friday called on China to stop its harassment of the Tiananmen protesters and their families.

On June 4, 1989, China's Communist government crushed a gathering of thousands of mostly young protesters in the city's landmark square. They had been demanding political reforms, including democracy. The number of those killed in the crackdown, or of those who disappeared in its aftermath, has never been determined.

Toner also said China should free the scores of people arrested in a crackdown on dissent that began early this year. Scores of lawyers, activists, writers and others have been detained, in what rights groups say appears to be an effort to make sure the popular uprisings seen in the Middle East do not spread to China.

The spokesman says the U.S. government also has expressed its concern with Chinese authorities over allegations that hackers based in China compromised the Google e-mail accounts of hundreds of users, including U.S. government officials.

China denies any responsibility for the attack. U.S. Secretary of State Hillary Clinton has called the allegations “very serious.”

On Friday, a report by Chinese military researchers said the country must prepare for cyber-warfare and develop defenses to computer attacks. Their report, published in an official newspaper, did not mention the Google case.

China maintains tight control over the Internet, which it says is necessary to protect social order and national sovereignty. It censors a wide range of web sites, such as those belonging to rights groups, Chinese dissidents and international news organizations, including VOA's. In recent months, it has blocked sites that discuss the uprisings in the Middle East.