The United States urged China on Tuesday to free activists swept up in a security operation ahead of the 25th anniversary of the Tiananmen Square crackdown on pro-democracy protests.
State Department spokeswoman Marie Harf said China was a growing country and should allow more space for political discussion about the authorities' suppression of a mass sit-in.
"We've very clearly called on the Chinese authorities to release all the activists, journalists and lawyers who have been detained ahead of the 25th anniversary," Harf told reporters.
"I think it's time to allow some more space, quite frankly, for discussion in their own country, particularly around this kind of anniversary," she added.
US authorities continually raise concerns about freedom of speech and expression with Beijing.
A monitoring service said several Google websites have also been blocked in China as authorities step up arrests and censorship before the anniversary.
And there is also a stepped-up police presence on Beijing's streets.
The Tiananmen pro-democracy protests were crushed on the night of June 3-4, 1989, when soldiers killed hundreds of unarmed civilians -- and by some estimates, more than 1,000.