The U.S. destroyed five Iranian oil tankers on Tuesday in response to fresh attempts by Tehran to strike U.S. warships in the Middle East in recent days, according to U.S. Central Command.

Since Friday, Iran has fired ballistic missiles at a U.S. aircraft carrier, a destroyer and at least one Marine ship, according to U.S. officials familiar with the attacks. All of the attacks have failed, Centcom said, but officials described some of them as close calls.

Iran's attempts to hit American naval assets are raising alarms that the regime is using more sophisticated weapons and could be getting assistance tracking the warships from China or Russia, the officials said.

In response to the attacks, the U.S. destroyed four Iranian tankers in the Gulf of Oman and one near Kharg Island, where Iran exports a majority of its oil, Centcom said. The crews of the Iranian tankers were directed to abandon ship before the strikes.

"Iran has used the tankers as part of a multibillion-dollar shadow network that funds the IRGC and its regional proxies," Centcom said, referring to the Islamic Revolutionary Guard Corps.

Iran later fired missiles at U.S. forces in Jordan, and the IRGC said in a statement that it was targeting jet fighters staged at the Muwaffaq Salti air base. Jordan's armed forces said the country intercepted 18 ballistic missiles and two additional missiles fell in unpopulated areas.

Centcom didn't respond to questions about whether some missiles hit the air base.

The renewed fighting comes after Iran first launched ballistic missiles at an aircraft carrier and a destroyer over the weekend. The U.S. responded to that attack by striking three other tankers Saturday to send a message that Iran's attacks wouldn't be tolerated.

The following days, Iran took aim at more warships, the officials said.

The attacks highlight Iran's willingness to go on the offensive as the U.S. blockade of Iranian ports weighs on the country's economy. They also risk escalating the conflict, since the U.S. has promised to take action against such attacks.

Iranian officials have claimed they are using new missiles with advanced features to target the American warships, according to Iran's state media. Such missiles could have electrooptical seekers, which enable them to maneuver toward a moving target using imagery, weapons analysts say.

However, Iran would still need to know the approximate location of U.S. warships when its attacks began, raising concerns that China and Russia could be helping Iran track the locations of American warships, officials said.

The fact that Iran is able to target warships at all after the U.S. degraded its ability to see the battlefield is a key concern, according to retired Vice Adm. John "Fozzie" Miller, who commanded U.S. naval forces in the Middle East. "They don't really have the capacity to reach out and find someone out in the Arabian Sea on radar any longer," he said.

In May, the U.S. sanctioned China-based entities for providing satellite imagery to Iran during the war. President Trump has so far played down concerns about China and Russia's assistance to Iran.

Iran unveiled a medium-range ballistic missile known as the Qassem Bassir with the seeker technology last year, according to John Caves, senior research associate at the Wisconsin Project on Nuclear Arms Control. Other Iranian missiles, like the Khalij Fars, also have the technology, he said.

U.S. officials hope that the blockade and crushing sanctions will bring the Iranian regime to its knees, but so far, the regime has refused to back down and is stepping up threats against U.S. Navy vessels. The U.S. has 19 warships supporting operations in the Middle East, according to a Navy official.

By striking tankers, the U.S. aims to further punish Tehran and crack down on the regime's ability to ship oil and fund its weapons programs.

While civilian ships aren't typically lawful targets, they lose their protected status if they contribute to an adversary's military action and if destroying them offers a definite military advantage, according to Mark Nevitt, associate professor of law at Emory Law School.

"Whether this test has been satisfied ultimately depends on the intelligence linking the oil financing to proxies and other factual matters-something that is acknowledged in the DOD's own law of war manual," Nevitt said.