Dr Shamsul Bari, an independent expert appointed by the U.N. Human Rights Council to report on Somalia, expressed concern over a rise in stonings and targeted assassinations of women's rights advocates, journalists and U.N. staff in a meeting with Somali Prime Minister Nur Hassan Hussein.
Citing the "deteriorating" human rights situation in the country, Dr Bari called on the interim Somali government to work to end the "cruel, inhuman and degrading" practices.
"I strongly condemn these recent executions by stoning," Dr Bari said in a statement.
The statement was released after Halima Ibrahim Abdirahman, a 29-year-old married woman, was stoned to death after she allegedly confessed to having had sex with a 20-year-old unmarried man in Eelboon, southern Somalia. The young man, who has not been identified, was sentenced to 100 lashes.
That came after a 20-year-old divorced woman accused of sleeping with an older, unmarried man was put in a public square, buried up to her waist and stoned to death in front of a crowd of 200 earlier this month in the town of Wajid, Somalia. Her boyfriend was given 100 lashes.
Abdirahman Hussein Abbas, a 33-year-old man accused of adultery, was stoned to death earlier this month in Merka, a port town south of Mogadishu. His girlfriend is set to face the same fate after giving birth to their child.
Large parts of Somalia are controlled by a group of Islamic militants loosely working together to overthrow the country's Transitional Federal Government under the banner of the 'Al Shabaab' movement.
Under Al Shabaab's interpretation of Sharia, Islamic law, crimes such as theft and adultery are punishable by floggings, amputation, torture or death.
Al Shabaab considers any person to have ever been married - including a divorcee - to be forbidden from having further relations. The punishment is often death by public stoning.
Al Shabaab executions first made international news a year ago when Amnesty International accused the Islamist group of stoning a 13-year-old rape victim to death in the southern city of Kismayo after she was accused of adultery. Al Shabaab claimed the girl was older and had been married.
Bashir Goth, a Somali analyst and the former editor of Awdal News, said Somalis are shocked by the lack of international interest in the actions of Al-Shabaab.