The United States is deploying military forces to the Middle East after Saturday's drone attacks on major oil sites in Saudi Arabia that the administration of President Donald Trump has blamed on Iran.

"The president has approved the deployment of U.S. forces which will be defensive in nature and primarily focused on air and missile defense," U.S. Secretary of Defense Mark Esper said at a news conference Friday.

Answering reporters' questions about the deployment, Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, described the troop deployment as "modest" and "not thousands."

Dunford said he planned to confer with U.S. Central Command and Saudi officials to work out details of the deployment, which he said would be announced next week.

Esper said troops would be primarily focused on air and missile defenses.

The United States will also accelerate shipment of military hardware to Saudi Arabia and the United Arab Emirates, he said.

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The defense secretary said the troop deployment to those nations is happening as Iran has engaged in a "significant escalation of violence" in the region.

On Wednesday, Secretary of State Mike Pompeo said that while Yemen's Iranian-backed Houthi rebels claimed responsibility for the Saudi oil-site attack, the "fingerprints" of Tehran's ayatollah were evident in the drone strikes.

Esper on Friday took that line of thinking further, saying, "The weapons used in the Iranian attack were Iranian produced and were not launched from Yemen as was initially claimed."

However, he emphasized that Saudi Arabia is leading the investigation into the attack. "We will keep them in the lead with regard to the forensics, so we need to let that play out, let the evidence play out," Esper said.

Iran's powerful Revolutionary Guard responded Saturday, with its chief commander saying it is ready for combat and "any scenario."

Gen. Hossein Salami, at a ceremony displaying pieces of an American drone Iran shot down in June, said that his forces have carried out "war exercises and are ready for any scenario."

He added: "If anyone crosses our borders, we will hit them."

The troop buildup in Saudi Arabia and the United Arab Emirates supplements sanctions against the Iranian banking system.

On Friday, Treasury Secretary Steve Mnuchin told reporters the Central Bank of Iran and the country's sovereign wealth fund, the National Development Fund, "will be cut off from our banking system."

"We are continuing the maximum pressure campaign," he said.

A picture taken on September 18, 2019 shows displayed fragments of what the Saudi defence ministry spokesman said were Iranian cruise missiles and drones recovered from the attack site that targeted Saudi Aramco's facilities, during a press conference in Riyadh. Fayez Nureldine / AFP - Getty Images

Esper expressed hope that the military show of force would "prevent further escalation."

"As the president has made clear, the United States does not seek conflict with Iran," Esper said. "That said we have many other military options available should they be necessary."

Saudi Arabia requested what the secretary described as "extra defensive support," he said, and it will "send a clear message that the United States supports our partners in the region."

The move was also made with commerce in mind, as the attack included as a target the world's largest oil processing facility.

The extra troops would help "ensure the support free flow or resources necessary to support the global economy," Esper said.