The conflict between Israel and Iran appeared to be spreading on Saturday to Iran’s energy infrastructure, raising fears about energy supplies from the Middle East.

Iran’s oil ministry blamed Israeli drones for attacking part of the South Pars natural gas field, one of the world’s largest, and a refinery, causing fires at both.

It is not clear how far Israel intends to go in attacking Iran’s energy facilities, a crucial source of export cash for the country as well as domestic energy that looks particularly vulnerable.

“This is a first salvo into energy and a warning shot that Israel is willing to hit Iranian energy infrastructure if Israeli civilians are targeted,” said Richard Bronze, head of geopolitics at Energy Aspects, a research firm.

Other Iranian installations are at risk, analysts say.

“There is one clear target that would make it very easy if Israel or the United States wanted to impact Iran’s oil exports,” Homayoun Falakshahi, senior analyst for crude oil at Kpler, a research firm, said during a webinar on Friday. “And this is Kharg Island.”

Nearly all of Iran’s oil exports leave from tankers at berths around Kharg Island, a small coral land mass in the northern part of the Persian Gulf off the Iranian coast, potentially making it a target in a protracted war, analysts say.