PORT HARCOURT, Nigeria April 29 (Xinhua) -- Nigerian Gunmen operating in the creek of oil rich Niger Delta region have abducted four officials of the country's National Agency for Food, Drugs Administration and Control (NAFDAC) along the Aba-Port Harcourt, a security source told Xinhua on Thursday.

The kidnapers also shot dead an operative of the agency, Emeka Obi Wohley, the security source said.

The source said the gunmen are demanding for a ransom of about 110,000 U.S. dollars.

One of the victims, who is heavily pregnant, was released on compassionate ground, the source added.

NAFDAC spokesperson Abubakar Jimoh confirmed the incident to Xinhua on phone.

He described the attack as shocking.

Obi Wohley was said to have traveled to his village in Imo State over the weekend and was expected to be back in the office on Monday morning.

Rivers State police spokesperson Rita Inoma-Abbey told Xinhua that she needed more time to get the details.

She, however, said a middle-aged man, Anayo Prince Wali, was kidnapped at the refuse dump opposite a gas plant along Airport Road, Rumuodomaya, Port Harcourt on Wednesday evening by four gunmen, who operated in a blue Toyota Camry car.

Inoma-Abbey said all police patrol teams were mobilized to search for the gang.

The police spokesperson added that more teams had been drafted to the nearby bush, searching for the kidnappers.

This brings to a total of 13 persons kidnapped this month alone within the Abia and Rivers states.

Abduction is common in Nigeria. Over 300 foreigners have been seized in the Niger Delta since 2006. Almost all have been released unharmed after paying a ransom.