Saudi Arabia has put on a display of drone and missile fragments that it said showed a weekend attack targeting the kingdom's crucial oil industry was "unquestionably sponsored by Iran."
Defense Ministry spokesman Colonel Turki al-Malki told a news conference in Riyadh on September 18 that 18 drones and seven cruise missiles struck from a direction that ruled out Yemen as a source.
"The attack was launched from the north and unquestionably sponsored by Iran," Malki said, adding that the exact launch site was still being investigated.
Yemen's Iranian-backed Huthi rebels had earlier said they were behind the September 14 attack that hit a Saudi oil field and the world's largest crude oil-processing plant.
Tehran has denied involvement in the air attack, and warned it would retaliate against any attack that targeted Iran.
Speaking to reporters on his plane before landing in the western Saudi city of Jeddah, U.S. Secretary of State Mike Pompeo described the alleged "Iranian attack" as an "act of war."
Meanwhile, President Donald Trump said "many options" were available including the "ultimate option" of war.
Hesameddin Ashena, an adviser to Iran’s president, tweeted that Saudi Arabia proved that "it knows nothing about where the missiles and drones were made or launched from."
In Riyadh, Malki showed off what was said to be a delta wing of an Iranian drone along with other weapons debris.
The Saudi Defense Ministry spokesman said that 18 drones had been fired at the Abqaiq oil facility, while four cruise missiles struck the Khurais oilfield and three others fell short of Abqaiq.
He said that the "precision impact" of the cruise missiles in the Khurais attack indicates "advanced capability beyond the Iran proxy's capacity."
"Despite Iran's best efforts to make it appear so, their collaboration with their proxy in the region to create this false narrative is clear, " Malki said, calling the attack "an assault on the international community."
Iranian Defense Minister Amir Hatami earlier said that the issue was very clear: "There has been a conflict between two countries," referring to Yemen and Saudi Arabia, which is leading a military coalition that has been battling the Huthis since 2015.
And President Hassan Rohani said 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.
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.
A spokesman for the Huthis, Yahia Sarie, threatened on September 28 to attack targets in the United Arab Emirates, a Saudi ally involved in fighting the rebels in Yemen.
Also en route to Saudi Arabia is a team of UN experts tasked with investigating the attack, Secretary-General Antonio Guterres said.
During a phone call, British Prime Minister Boris Johnson agreed with Trump that there must be "a united diplomatic response from international partners" to the weekend attack, according to Johnson's office.
Britain has condemned the strikes on the heart of the Saudi oil industry, but said it was too early to say who is to blame.
In a September 17 speech at the Heritage Foundation think tank in Washington, U.S. Vice President Mike Pence said the United States was consulting with its allies before Trump determines "the best course of action in the days ahead."
Unnamed U.S. officials were quoted as saying that the September 14 attack that struck a Saudi oil field 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.
Meanwhile, the Saudi kingdom announced it had joined a U.S.-led naval mission to patrol the waters in the Persian Gulf.
And Iran's semiofficial Iran Front Page website reported that 200 frigates and speedboats will take part in a September 22 parade in the Gulf to mark the beginning of Iran-Iraq war.
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 later told reporters the unspecified, punitive economic measures would be unveiled within 48 hours.
Iran's Foreign Minister Mohammad Javad Zarif, himself under U.S. sanctions since July, described the sanctions as "illegal" and "inhuman.”