Acting President Raimundo Pereira and Prime Minister Carlos Gomes were taken into custody last week following a military coup. Gomes was the leading candidate in a runoff election scheduled for later this month.
Christophe Tinguely, from the International Committee of the Red Cross, said he was able to meet with both leaders earlier this week under the terms of an agreement with detaining authorities.
"The detainees were provided with medical supplies, clothing and hygiene items," the ICRC said in a statement. "In addition, they were given the opportunity to send news to their close relatives."
Opposition leaders met last weekend with coup leaders to announce the formation of a transitional national council. The group said an interim president would rule the country until presidential and parliamentary elections.
The African Union said Tuesday it suspended the membership of Guinea-Bissau until constitutional order is restored in the West African country. The coup was widely condemned by members of the international community.