WASHINGTON – Iran’s seizure of a British oil tanker in theStrait of Hormuz on Friday further escalated tensions that have been building for weeks in the Middle East.

The tanker seizure followed a dispute this week between Iran and the Trump administration over claims the U.S. had shot down an Iranian drone in the strait.

Here’s what we know:

What happened?

IFARS, Iran's semi-official news agency, confirmed the capture of the British vessel on Friday by the Islamic Revolutionary Guard Corps, or IRGC, and said Iranian naval forces detained a Liberian-flagged ship but later released it.

The IRGC said its naval forces had seized the Stena Impero tanker for allegedly violating maritime rules and regulations in the Persian Gulf, the semi-official FARS news agency reported. The ship was escorted to the Iranian coastal waters in Hormuzgan province, the IRGC said, and control was transferred to the Ports and Maritime Organization "for further legal procedures and investigations."

The company that owns the tanker said in a statement that the vessel, with 23 people aboard, was approached by "unidentified small crafts" and a helicopter in the Strait of Hormuz, Reuters reported.

"We are presently unable to contact the vessel which is now heading north towards Iran," the company said.

There were no reported injuries, the company said.

At the White House, President Donald Trump declined to say whether Iran's actions crossed a "red line" or how the U.S. might respond. But hours later, the Pentagon said it had authorized the movement of additional troops to Saudi Arabia as an "additional deterrent."

U.K. Foreign Secretary Jeremy Hunt called the capture of British-flagged and Liberian-flagged vessels "unacceptable."

What is the Revolutionary Guards?

Iran’s Revolutionary Guards Corps is a powerful security organization founded in the aftermath of Iran's 1979 Islamic Revolution. It has a vast political and economic power base that extends to Iran's armed forces, as well as its strategic industries from oil to agriculture.

The IRGC also presides over Iran's ballistic missiles and nuclear programs.

In May, the Trump administration designated the corps a foreign terrorist organization and imposed sanctions on its assets. The move reflected Washington's increasingly aggressive stance toward Tehran.

The drone controversy

The day before the British ship was seized, Trump announced that the USS Boxer destroyed an Iranian drone that came within 1,000 yards of the warship and ignored multiple calls to stand down.

Neither Trump nor the Pentagon spelled out how the Boxer destroyed the drone or provided any video or other evidence from the incident. Several U.S. officials said the ship used electronic jamming to bring it down rather than hitting it with a missile.

Iran, however, said that all of its drones in the Persian Gulf had safely returned to their bases and suggested the U.S. had destroyed its own drone by mistake.

Trump said Friday there is “no doubt" that a U.S. warship destroyed an Iranian drone. National security adviser John Bolton said, “There is no question this was an Iranian drone and USS Boxer took it out.”

More:Trump says U.S. destroyed Iranian drone that was threatening Navy ship USS Boxer

More drone drama

This week’s incident was not the first drone drama in the region this summer.

Iran's Revolutionary Guards shot down a U.S. surveillance drone in June, a bold strike that drew a stern warning from Trump and prompted top Pentagon officials to formulate military response options.

Iran said the drone was destroyed over its coast and said the incident sent a "clear message" that the Persian Gulf nation was ready to defend itself from what it views as Western aggression. The Pentagon, however, said the incident played out in international waters over the Strait of Hormuz.

Regardless, the U.S. prepared to make a retaliatory strike on Iran, but Trump canceled the attack at the last minute.

Trump said U.S. forces had been “cocked and loaded,” but that he called off the attack just 10 minutes before it was to take place after learning that 150 Iranians would die in the strike.

More:'You'll soon find out' if US retaliates after Iran shoots down drone, Trump warns

Other tensions

Tensions between the U.S. and Iran have been building for months after the Trump administration pulled out of a 2015 nuclear deal negotiated by President Barack Obama’s administration and other world powers.

Those tensions escalated in June, when two tankers reported they had been attacked about 25 miles off the southern coast of Iran.

The Front Altair, loaded with the flammable hydrocarbon mixture naphtha from the United Arab Emirates, radioed for help as it caught fire. A short time later, the Kokuka Courageous, loaded with methanol from Saudi Arabia and Qatar, also called for help.

The U.S. Navy's Fifth Fleet said it received two distress calls and sent the guided-missile destroyer USS Bainbridge to the scene.

No nation or group claimed responsibility, and Iran denied it was involved in the attack.

But Secretary of State Mike Pompeo told reporters the attack was the work of Iran. Pompeo said the assessment was based in part on U.S. intelligence, the expertise needed for the operation and other recent incidents in the region, which the U.S. also has blamed on Iran.

More:'We don't take it lightly': What we know about oil tanker blasts and Donald Trump's escalating rhetoric on Iran

Other ships attacked

The June attacks drew parallels to an earlier attack against oil tankers off the coast of the United Arab Emirates.

Saudi Arabia said in May that four oil tankers were sabotaged, which caused "significant damage" to the vessels. One of the ships was en route to pick up Saudi oil to take to the U.S.

An investigation blamed explosive sea mines, and Saudi Arabia and the United States blamed Iran. Iran denied involvement, although Iranian-backed rebels in Yemen have launched missile and drone attacks on Saudi Arabia.

More:How to turn Iran’s tanker mischief against the Islamic Republic

Sanctions

With tensions mounting, the Trump administration announced Friday it is imposing new sanctions on a senior member of the Iranian-backed militant group Hezbollah.

The administration also announced a $7 million reward for information leading to the capture of 25-year fugitive Salman Raouf Salman and described the actions as part of itd "maximum pressure" campaign on Iran.

The administration announced its actions on the 25th anniversary of an attack Salman is accused of ordering on a Jewish center in Buenos Aires, Argentina. The attack killed 85 people and wounded hundreds of others.

Since then, the U.S. and other nations have accused Salman of plotting other attacks from a base in Lebanon. Officials believe he is still in the Middle East, but do not know exactly where.

Contributing: John Fritze, David Jackson, Donovan Slack, Nicholas Wu, Doug Stanglin, Kim Hjelmgaard