Nigerian troops killed 12 men caught stealing crude oil from a pipeline in the southern state of Delta, the head of a government task force on pipelines said on Sunday, Reuters reported. Siphoning oil from pipelines, a practise known locally as bunkering, is common in the Niger Delta, a vast region of mangrove creeks and swamps that accounts for almost all of Nigeria's 2.4 million barrels per day (bpd) production of crude. Government official Isiaka Pachiko said troops on patrol in remote Oghara community stumbled on a group of bunkerers on Saturday who had heavy drilling equipment and four trucks ready to be loaded with oil. A gunbattle broke out and 12 of the suspected oil thieves were killed, three were injured and five were arrested, Pachiko said. He did not mention any casualties among the troops. The Nigerian security forces have been cracking down on bunkering this year, and industry officials estimate that large-scale oil theft has dropped from 100,000 bpd earlier this year to about 20,000 now because of a heavier military presence. Some oil industry workers suspect that frustration over the crackdown may be one of the reasons behind a recent spate of pipeline attacks. A suspected dynamite blast at a Royal Dutch Shell pipeline in neighbouring Rivers state on Dec. 20 killed 11 people and cut output by 180,000 bpd.