The International Committee of the Red Cross has made a formal request to the Burmese government for access to those detained in connection with recent protests.
The ICRC released a statement Thursday noting that the Burmese military government claims to have released hundreds of detainees in recent weeks. But the group says dozens of families have approached the Red Cross recently, seeking contact with missing relatives.
Hundreds of people imprisoned during the violent crackdown on demonstrators in September are still believed to be behind bars.
More than 100 Buddhist monks marched this week in central Burma in the first protests since the September crackdown.
Chinese state media quoted a foreign ministry spokesman as saying China hopes all parties in Burma will exercise restraint. But spokesman Liu Jianchao dismissed the idea of putting pressure on Burma.
United Nations envoy Ibrahim Gambari recently made a six-country Asian diplomatic tour to urge China and other countries to increase pressure on Burma's military government.
Gambari will visit Burma from November third to eighth in another bid to foster national reconciliation. It will be his second visit there since the crackdown.