UPDATE 4-Nigeria rebels attack oil facility, hijack tanker

* Militants say attack Chevron oil manifold

* Rebels also hijack chemical tanker, kidnap six

* Violence cuts at least 273,000 bpd of oil output

(Adds military spokesman, paragraphs 2-3, 9)

By Randy Fabi

ABUJA, July 6 (Reuters) - Nigeria's main militant group said on Monday it had sabotaged a Chevron (CVX.N) oil facility and seized a chemical tanker and six crew members, the latest in a string of attacks in Africa's biggest energy producer.

The Movement for the Emancipation of the Niger Delta (MEND) said it had attacked Chevron's Okan manifold late on Sunday in the southern Delta state, hours after it sabotaged an oil well head operated by Royal Dutch Shell (RDSa.L). The military confirmed the attack.

"The criminals attacked another pipeline in Delta state yesterday. The pipeline belongs to Chevron," said Colonel Rabe Abubakar, spokesman for the military task force.