Unidentified gunmen killed two workers and kidnapped two others at a water plant in southeastern Libya early on Saturday, the second attack targeting water facilities in two days, officials said.
"An armed attack was carried out by terrorist groups on the Tazirbu site causing havoc, looting, killing and terrorising families, children and the workers who ensure the supply of water to cities," said a statement from the Great Man-made River Project, a pipe network supplying water to the Libyan Sahara.
An engineer and a guard were killed and two guards were kidnapped in the raid. The assailants also stole cars and supplies from the site, the statement added.
On Friday, members of an unidentified armed group kidnapped three Filipinos and one Korean employed as technicians at the Al-Hassouna plant, part of the same water network connecting desert wells to towns and cities in northern Libya.
The Al-Hassouna and Tazirbu sites are about 1,000 km (620 miles) apart, an official said.
It was not clear who carried out either of the attacks, but armed groups including Islamist militants linked to al Qaeda and Islamic State have a presence in Libya, especially in remote desert areas.