The Foreign Office on Monday said it is investigating reports concerning the abduction of Pakistani engineer Ayaz Hussain Jamali in South Sudan by rebels.

"We have been informed about the reported abduction," FO spokesman Nafees Zakaria told Dawn.com, adding that the FO does not have much to share at the moment.

Read more: Pakistani engineer reportedly kidnapped by rebels in South Sudan

"We do not have a mission in South Sudan. Our mission in Ethiopia's Addis Ababa is working with the South Sudan government to provide us with a clear picture of the situation," added the spokesman.

According to reports, South Sudanese rebels said on Monday that they had kidnapped four oil workers, including a Pakistani national, in a bid to force a Chinese and Malaysian consortium 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.

Fighters loyal to former vice president Riek Machar said they had seized the four oil workers from Upper Nile state – the second group of oil workers abducted this month.

There was no immediate comment from DAR, a consortium which includes China National Petroleum Corporation (CNPC), China's Sinopec and Malaysia's Petronas.

South Sudan, which split away from Sudan in 2011 after decades of conflict, has been mired in civil war since President Salva Kiir sacked Machar in 2013.

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

South Sudan's government said it was using "diplomatic channels" to negotiate the workers' release and accused the rebels of demanding a ransom.

Rebel spokesman Lam Paul Gabriel had dismissed that allegation.

"There are no conditions for their release, but we want to make it clear to their country of residence and the government that we do not want their company to operate in South Sudan," he told Reuters.