Analysts watching the world’s oil markets were fearing Friday that Iran would target energy infrastructure in countries like Saudi Arabia as retaliation for the U.S. killing Gen. Qassem Soleimani.

The concerns come as Brent crude, the international benchmark for oil prices, rose about 1 percent, according to FOX Business." While the reaction was measured, oil watchers say further escalation in the region could send prices higher.

Iranian President Hassan Rouhani already has vowed to “take revenge” for the death of Soleimani, the former head of the Islamic Revolutionary Guard Corps' elite Quds Force.

“They're not going to confront the U.S. directly but they will perhaps attack Saudi tankers again, maybe Saudi oil refineries again," John Tirman, the executive director of the Massachusetts Institute of Technology Center for International Studies, told Al Jazeera.

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"The fact is that Iran will come back and hit U.S. assets or the assets of U.S. allies in the region, and they will do so repeatedly over a period of time," he added.

Iran has been particularly active in the Persian Gulf area over the past year.

In addition to seizing ships in the Strait of Hormuz, Iran has been accused by the U.S. of launching cruise missiles and drones from its territory to bombard Saudi Arabia's oil installations.

An attack in September 2019 on a facility owned by Saudi Arabia’s Aramco state-run oil company knocked out 5.7 million barrels of daily oil production — or more than 5 percent of the world's daily crude production.

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“Don’t be surprised if the Iranians launch a bunch of missiles at Saudi and UAE especially at U.S. bases but also oil facilities,” Ilan Goldenberg, the Middle East Security Director at the Center for a New American Security, tweeted Friday. “They surprised us in September with their accuracy but they purposely tried to keep the damage to a minimum. This time they may not do that.”

Jason Bordoff, a former White House energy advisor to President Obama, described the killing of Soleimani as a “seismic event in the region.”

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“Iran's response will be severe & deadly,” he tweeted. “And certainly may include escalating attacks on energy infrastructure,” adding that the Saudi attack in September “was just the beginning."

Fox News' Lucas Tomlinson contributed to this report.