KADUNA, Nigeria (Reuters) - Two Americans and two Canadians have been freed after being kidnapped in the northern Nigerian state of Kaduna, a police spokesman said on Saturday, as it emerged that five oil workers had been abducted in the southern Niger Delta region.

The Americans and Canadians were ambushed by unknown gunmen on Wednesday while traveling from the town of Kafanchan in Kaduna state to the capital, Abuja. Kafanchan is more than three hours’ drive northeast of Abuja.

In a separate incident, police in the Delta state said five Nigerian oil workers from local firm Sahara Energy were kidnapped on Thursday. Delta state police said no arrests had been made.

Kidnapping, usually for ransom, is common in parts of Nigeria, though abductors usually target other Nigerians. However, the kidnapping of foreigners is not uncommon.

Mukhtar Aliyu, a spokesman for Kaduna state police, said the Americans and Canadians were freed on Friday.

“It was the efforts of the police, through the directive of the inspector general of police, that yielded their release last night,” he said. Aliyu said no ransom was paid.

The road connecting Abuja and Kaduna has long been targeted by kidnappers. Two German archaeologists were abducted in the region last February; they were later freed.