Guwahati, Oct 27 - A Bodo militant was killed and three arrested Tuesday as security forces stepped up the offensive to rescue an Andhra Pradesh engineer abducted from Assam's Kokrajhar district, as a prominent Bodo group issued an appeal for his release.

A special police commando team accompanied by soldiers was involved in a massive search operation to rescue P. Krishna Rao, kidnapped by suspected militants of the National Democratic Front of Bodoland (NDFB) from a highway construction site near Joypur in Kokrajhar district on Oct 16, police said.

On Tuesday, security forces exchanged gunfire with NDFB militants near a thickly forested area in Panbari in Chirang district, about 200 km west of Assam's main city Guwahati.

"We managed to arrest three NDFB militants in separate raids in the past two days, besides killing another early Tuesday in an encounter.

"Two NDFB militants were killed in an adjoining district over the weekend in similar operations to rescue the kidnapped engineer," a police official said.

Rao was the project manager of Gayatri Company, a private infrastructure firm engaged in constructing a four-lane highway in a 63-km strip in Kokrajhar district.

"Operations are continuing in full swing although we are yet to get any clue about Rao's whereabouts," state Agriculture Minister Pramilla Rani Brahma said.

The minister is overseeing rescue operations in the area.

"We have been raiding various possible locations in the area and the search is on in full steam," the minister said.

The Bodo Sahitya Sabha, the apex literary body in the region, appealed to the abductors to release Rao.

"We want that whoever kidnapped Rao should release him immediately. Such cases bring a bad name to the state and its people. We shall try our best to do whatever possible to secure his release," Kameswar Brahma, president of the Sabha, told IANS.