LAGOS, Nigeria --- A day after declaring war in Nigeria's oil-rich delta region, the country's main rebel group said Monday it was continuing its "destructive sweep" against oil facilities in Rivers State, CNN reported.

The Movement for the Emancipation of the Niger Delta said its militant forces "stormed" the Alakiri flow station complex, operated by the Shell Petroleum Development Company, set fire to the facility and "razed it to the ground," CNN reported.

A day earlier, MEND had warned all international oil workers to evacuate  their facilities because the group planned to "bring these structures to the ground."

"The foolhardy workers and soldiers who did not heed our warning perished inside the station," MEND said, referring to the Shell complex.

Shell confirmed that gunmen attacked its Alakiri flow station, gas plant and field logistics base, southwest of Port Harcourt. The attack killed a guard and wounded four others.

"SPDC (Shell Petroleum Development Company of Nigeria) is saddened by this fatality and our thoughts are with the family of the late station guard," company spokeswoman Caroline Wittgen said in a written statement.

As a precaution, Shell has shut down its facilities in some field locations, but would not give any more details "for security reasons."

"Shell is aware of the difficulty the security situation places on staff, and continues to monitor developments," Wittgen said.

Nigeria's military could not be reached by CNN for comment.

The latest claim by MEND comes a day after it said it attacked oil flow stations and pipelines in response to what it said were "unprovoked" attacks by Nigerian government forces on Saturday, CNN reported.

MEND said it intercepted 22 Nigerian soldiers at the Soku Gas Plant, Chevron Platform at Kula on Sunday. It said the soldiers were "killed and dispossessed of their weapons." The group also said it blew up several points on the major crude trunk pipeline at Nembe Creek.

A Chevron spokesman told CNN that it has received reports of shooting near its Robertkiri facilities in Rivers State, but there is no evidence that the attack was directed at Chevron. No Chevron employee was hurt as a result of the attack, company spokesman Scott Walker told CNN in an e-mail. But he noted that initial reports suggested two contractors "might have died" in the incident.

MEND has also warned of impending attacks against international companies' oil and gas-loading vessels. The rebel group seeks a greater share of Nigeria's oil wealth for people in the delta, where more than 70 percent of the population lives on less than a dollar a day, CNN reported.

Nigeria is the fourth-largest supplier of oil to the United States, and attacks by rebels have helped fuel the spike in crude oil prices.