South Sudan promised to increase security at oil installations on Tuesday, days after rebels kidnapped four oil workers including a Pakistani national in an effort to force foreign companies to leave the country.

A resident of Sindh's Badin district, Jamali was an employee of DAR Petroleum Operating Company. Ayaz's younger brother, Babar Jamali, who also works in the same oil company, informed the family in Badin that Ayaz was kidnapped over a week ago. The foreign ministry also stated earlier that it is looking into Jamali's reported abduction.

Know more: FO investigating reports of Pakistani engineer’s abduction in South Sudan

Fighters loyal to former vice president Riek Machar seized the workers employed by DAR Petroleum Operating Company from Upper Nile State on Saturday - the second group of oil workers abducted this month.

Two Indian employees of the Ministry of Petroleum are also among those who have been kidnapped.

During a visit to Paloch, the country's main oilfield, Petroleum Minister Ezekiel Lol Gatkout sought to reassure a gathering of mainly Indian foreign oil workers that security would improve.

"We have taken a decision that you are protected one hundred percent. Don't worry ... you will see a lot of people here with guns," he said at the plant in Upper Nile.

South Sudan has been mired in civil war since 2013 and the unrest threatens the plans of the world's youngest country to more than double crude production to 290,000 barrels per day in the 2017/2018 fiscal year.

The Dar consortium includes China National Petroleum Corporation (CNPC), China's Sinopec and Malaysia's Petronas.

"From today onward, this thing is not going to happen again. Even if one person is going out for a small operation in the fields, he will be escorted with 50 soldiers."

The fighting in South Sudan has forced 3 million people to flee their homes, split much of the population along ethnic lines and paralysed agriculture, leaving the country facing famine, according to the United Nations.