The speaker of Crimea's parliament said Russia and its state-owned energy giant Gazprom should control oil and gas production in the semi-autonomous Ukrainian region.
Vladimir Konstantinov said Crimeans were protecting the region's oil industry sites amid the political turmoil gripping Ukraine.
Around 60% of Crimea's population is ethnically Russian and Russia has financial interests in the country.
After a revolution ousted Kremlin-allied President Viktor Yanukovich, Russia's President Vladimir Putin deployed thousands of troops into Crimea – described by the European Union and US as an act of aggression.
"Russia, and Gazprom, should take care of the oil and gas production. It's not our issue," Konstantinov said in comments to the RIA news agency in Russia, adding that "these are our oilfields and we will fight for them".
Crimea's regional parliament voted by a majority to split from Ukraine if a referendum of the local population on 16 March backs independence.
But leaders of the G7 demanded in a joint statement that the referendum, taking place under the watchful eyes of Russia's troops, is not legal, deeply flawed and should be stopped.
They warned action would be taken unless Russia stops trying to change the status of Crimea.
The EU and US has already placed visa sanctions on Russia and warned that economic sanctions will follow unless the Ukraine crisis is de-escalated.