Senator Lindsey Graham called out Donald Trump for his "measured response" to Iran.

Several US lawmakers urged caution Tuesday in countering recent attacks on Saudi oil installations, but Trump loyalist Senator Lindsey Graham branded the incident an "act of war" that merits a decisive response.

Graham said it was "clear" that such a sophisticated attack -- drones firing missiles into the world's largest processing plant and an oilfield in Saudi Arabia -- could only have originated with direction and involvement from the "evil regime in Iran."

"This is literally an act of war and the goal should be to restore deterrence against Iranian aggression which has clearly been lost," Graham said in a statement.

The Republican lawmaker and trusted Trump ally tweeted that Washington should consider an attack on Iran's oil refineries in response, a move that he said "will break the regime's back."

Graham has been a defense hawk for years, and he noted that Trump's "measured response" to Iran shooting down an American drone in June "was clearly seen by the Iranian regime as a sign of weakness."

Trump pushed back on Twitter, saying: "No Lindsey, it was a sign of strength that some people just don't understand!"

A classified briefing book on the attacks was made available to US senators in a secure location in the US Capitol.

Other Republicans senators including Marco Rubio and Ron Johnson said they fully believe Iran was responsible for the Saudi strike.

But Jim Risch, the Republican chairman of the Senate Foreign Relations Committee, cautioned against launching a rapid-response military attack on the Islamic republic.

"We're not anywhere near that point. We're still in the analysis situation," he said, adding that he has encouraged lawmakers to study the classified evidence on the attack in Saudi Arabia.

Members of Congress have been divided over Riyadh since the murder last October of journalist Jamal Khashoggi, who wrote pieces critical of the kingdom, and revelations that he was killed by Saudi agents.

While Graham appeared quick to support Riyadh on Tuesday, earlier this year he led the charge to block some US arms sales to the kingdom over Khashoggi's brutal murder.

"There is no amount of oil that you can produce that will get me and others to give you a pass on chopping somebody up in a consulate," Graham said in June.