PARIS (Reuters) - Two French aid workers were kidnapped on Sunday evening in the northeast of the Central African Republic, the latest in a string of kidnappings in the region.

They were seized in the town of Birao on the border with Chad and Sudan, Christian Lombard, co-director at French aid organisation Triangle, told Reuters on Monday. Two other French aid workers have been kidnapped in the past few weeks, in Chad and Sudan's Darfur.

France's foreign ministry said in a statement it "condemns this latest criminal act which once again hits aid workers in a region where their assistance to the population is crucial," and demanded the aid workers be released.

It said its crisis unit was in close contact with the concerned parties, without saying who had carried out the kidnapping.

Earlier this month, a Frenchman working for the International Committee of the Red Cross was kidnapped by armed men in Chad, leading the charity to temporarily suspend its activities in the region.

In October, another French citizen working for the ICRC was kidnapped in Sudan's Darfur region. Both aid workers are still being held captive, the ICRC said.

The Central African Republic is one of Africa's poorest and most isolated countries, with a weak government struggling to end several years of internal rebellions.