Three Red Cross workers who were kidnapped by armed men in the southern Yemeni province of Abyan have been safely released, the organisation has said.

The three staff members for the International Committee of the Red Cross (ICRC) had been held since Monday morning when the armed men stopped their ICRC-marked vehicle in the vicinity of Jaar, near the southern port city of Aden, the organisation said in a statement on Thursday.

The two international staff from Kenya and Switzerland, and a locally hired employee were on their way back from a field trip.

Cedric Schweizer, who heads the ICRC delegation in Yemen, said the staff members are now safely back in Aden.

"We are relieved and extremely happy to have our colleagues back with us," Schweizer said, who thanked "all those who gave us their support unconditionally with the aim of getting our colleagues back safe and sound".

Yemen's president warned last week that the al-Qaeda branch in the country was expanding and using assassinations and abductions of foreigners as a way to challenge central authority.

The ICRC has been operating in Yemen since 1962, delivering aid for civilians affected by conflicts in the impoverished Arab nation that has struggled to beat back al-Qaida fighters and the country's political divisions.

The Geneva-based humanitarian organisation has more than 200 staff in the country, including 50 international employees, working in Sanaa, Aden, Saada, Amran and Taiz.

They provide health care, deliver relief assistance and work to improve water supplies.

In Jaar, the ICRC has a surgical team providing support to the surgical unit of a general hospital.

ICRC delegates also visit detainees and help Yemeni families keep in touch with loved ones detained abroad.