KHARTOUM, Sudan — Unknown armed men have kidnapped four Chinese workers in Sudan's troubled Darfur region, the state news agency SUNA said on Sunday.

The assailants abducted the Chinese — one engineer and three drivers — together with five Sudanese colleagues late on Saturday near al-Fasher in North Darfur, SUNA said, adding that all had been working for a Chinese road company.

Authorities were pursuing the kidnappers with 18 military vehicles, SUNA said, without giving further details.

China is Sudan's biggest ally and largest investor in the oil industry there as well as in Khartoum's arch rival South Sudan. Chinese firms are ever-present in Sudan, as most Western firms shun the African country due to a U.S. trade embargo.

Sudan has sought to assure China that it would protect its firms after rebels in Sudan's main oil-producing state of South Kordofan kidnapped 29 Chinese workers in January 2012. They were released almost two weeks later.

China also gives extensive aid to Sudan, even in dangerous places such as Darfur where law and order has collapsed since mainly non-Arab tribes took up arms against the government in Khartoum, which they accuse of neglecting them.

Gunmen often kidnap foreigners in Darfur to demand a ransom for their release.

In December, a Sudanese court handed out life sentences to four Sudanese for killing a Chinese worker during a raid on a workers' oil camp, the state-linked Sudanese Media Center said. It gave no details.

Beijing has tried to help Sudan overcome the loss of most oil reserves, the lifeline of the economy, when South Sudan became independent in 2011.

Last week, Sudan's Finance Minister Ali Mahmoud told Reuters China had granted the country a $1.5 billion loan at a time when Sudan is trying to stop a slide of its currency.