More than 5,400 people have been killed in clashes since December 2005 in an ethnic conflict that has claimed more than 60,000 lives since 1972. The International Committtee of the Red Cross (ICRC) said it has recorded 34 abductions by unknown persons throughout the country in the past three weeks.
Sri Lanka's rights record is due to be discussed when the UN Human Rights Council meets in Geneva from September 10-28.
The ICRCs findings came as Sri Lanka last week appointed a committee to probe allegations of child recruitment by an ethnic Tamil militia linked to the government.
Sri Lanka has come under severe criticism from local and international rights groups for allegedly colluding with the breakaway Tamil rebel faction known as the Karuna group. Colombo has denied the charge.
The London-based rights group Amnesty International said last month that hundreds of people disappeared in Sri Lanka in the past year and more than 5,700 such cases from the past three decades were under UN rev