Saudi Arabia says it has joined a U.S.-led coalition to patrol the waters in the Persian Gulf amid rising tensions in the region after an attack targeting its crucial oil industry, while Iran's president said the attack was a warning to Riyadh to end its intervention in Yemen.
Saudi's decision to enter the International Maritime Security Construct came ahead of a planned visit to the kingdom by U.S. Secretary of State Mike Pompeo.
Washington has accused Iran of being behind the attack, while Saudi Arabia already has said that "Iranian weaponry" was used.
Iran denies involvement in the air attack, which was claimed by Iranian-backed Yemeni Huthi rebels, who said drones were used.
Iranian Defense Minister Amir Hatami on September 18 reiterated Tehran's claim that it had no involvement in the attacks, the semiofficial Tasnim news agency reported.
President Hassan Rohani said on September 18 that Huthis targeted Saudi oil facilities as a "warning" about a possible wider war in response to the kingdom's U.S.-backed intervention in Yemen.
"The Yemenis...haven't hit a hospital, they haven't hit a school.... They just hit an industrial center...to warn you," Rohani said after a cabinet meeting.
"Learn lessons from this warning and consider that there could be a war in the region," he added.
The Saudi Defense Ministry said it will hold a news conference later on September 18 to present "material evidence and Iranian weapons proving the Iranian regime's involvement in the terrorist attack."
Pompeo is en route to Saudi Arabia to "discuss our response" to the attack on Saudi oil facilities over the weekend.
The State Department said Pompeo will meet with Saudi Crown Prince Muhammad bin Salman in Jeddah on September 18 to discuss "the recent attack on the kingdom's oil facilities and coordinate efforts to counter Iranian aggression in the region."
Pompeo will then go to Abu Dhabi, United Arab Emirates, to hold talks with Crown Prince Muhammad bin Zayed.
In a note sent this week to the United States via the Swiss Embassy in Tehran, Iran warned that "in case of any aggression against Iran, that action will face an immediate response from Iran and the response won't be limited to its source," according to the state news agency IRNA.
The Swiss Embassy represents U.S. interests in Iran.
In a September 17 speech at the Heritage Foundation think tank in Washington, U.S. Vice President Mike Pence said the United States was reviewing evidence that suggests Iran was behind the attack, and was consulting with its allies before President Donald Trump determines "the best course of action in the days ahead."
Three unnamed U.S. officials were quoted as saying that the September 14 attack that struck a Saudi oil field and the world's largest crude-oil-processing plant originated in southwestern Iran and involved both cruise missiles and drones.
The strikes knocked out 5.7 million barrels of crude-oil production per day for the Saudi kingdom, or about 5 percent of the world's daily production.
On September 18, the U.S. State Department called on Americans to "exercise increased caution" while traveling to Saudi Arabia, a travel advisory posted on its website said.
Relations between Washington and Tehran have soured since Trump withdrew from the Iranian nuclear deal last year and reimposed sanctions over the country's nuclear and ballistic-missile programs.
Amid escalating tensions, Trump said on September 18 that he had ordered Treasury Secretary Steven Mnuchin to "substantially increase sanctions" imposed on Iran.
He did not give details on the move.