CAIRO — Five United Nations employees have been released after they were kidnapped in Yemen 18 months ago, a U.N. spokesman said in a statement on Friday.

U.N. Secretary-General Antonio Guterres is “delighted” and “relieved that their ordeal and the anxiety of their families and friends have finally come to an end.”

Guterres called for the perpetrators to be held accountable, without pointing fingers at any group. He also expressed solidarity with other people still held against their will in Yemen.

Available information suggests that all five U.N. security staff members are in good health, the statement added.

The employees were kidnapped by gunmen believed to be linked to al-Qaida in the southern province of Abyan while they were on their way back to the government’s temporary capital, Aden, after a field mission.

Al-Qaida and the Islamic State terrorist groups are active in Yemen, taking advantage of the poor security situation in the country.

Yemen has been roiled by a devastating power struggle between the government and the Houthi rebels, who seized the capital Sanaa and other areas since late 2014.

Last month, a United Nations aid employee was killed in the southwestern province of Taiz when an unknown gunman on a motorbike shot him.