US equity futures and Asian stocks declined on Thursday, extending a volatile week, as oil prices rallied after an attack on two tankers in Iraqi waters underscored the threat to energy assets in the Middle East.

Contracts for the S&P 500 Index were down 0.8% while a gauge of Asian shares dropped as much as 1.1% in early trading. Brent crude climbed back toward $100 a barrel as the assault on tankers prompted Iraq to stop operations at its oil ports. Separately, Bahrain said Iran targetedBloomberg Terminal its fuel tanks.