Jakob Kellenberger, president of the International Committee of the Red Cross, wrote to Putin to unblock negotiations that have stalled over ICRC demands for full access to detainees.
The neutral agency had to suspend visits two years ago because "there were too many obstacles to conducting them properly," ICRC spokeswoman Annick Bouvier said.
ICRC delegates met and registered 3,220 detainees in the region from May 2000 until the visits were suspended in September 2004, Bouvier said. The agency knew there were more detainees but was unable to count them because of lack of access, she said.
The agency has been negotiating with Russian officials since it suspended the visits, but the talks have failed, Bouvier said.
The Geneva-based ICRC, which visits prisoners of conflict under the Geneva Conventions on the conduct of warfare, demands that it have private access to any detainee, be able to make follow-up visits to all detainees and be informed of all places of detentions, the AP reports.
In his June 13 letter to Putin, Kellenberger said the ICRC's conditions for detainee visits were accepted by nearly 80 countries where it operates, Bouvier said.
ICRC delegates visited 528,611 detainees held in 2,594 places of detention in 76 countries last year, Bouvier said.