Here is a recap:

- 'Credible threat' -

On May 5, the United States says it is sending an aircraft carrier strike group and a bomber task force to waters near Iran in response to "indications of a credible threat by Iranian regime forces."

The Pentagon also sends B-52 bombers to the region and, later, an amphibious assault ship and Patriot missile defence battery.

US officials do not give more details of the threats but the move comes amid heightened tensions over Iran's nuclear programme.

Washington reimposed sanctions on Iran last year after quitting a 2015 deal meant to control its nuclear drive.

On May 8, Iran announces a halt to certain commitments under the agreement, including increasing enriched uranium and heavy water production.

US President Donald Trump responds with new sanctions on Iran's steel and mining sectors.

- Tanker 'sabotage' -

On May 12, the United Arab Emirates says four commercial oil tankers had been targeted by "acts of sabotage" in Gulf waters off its coast.

Saudi Arabia says later two of its oil tankers suffered "significant damage" but no casualties or oil spill.

The other vessels were Norwegian and Emirati.

Washington and Riyadh blame Tehran, which denies involvement.

A UAE investigation finds later that a "state actor" was likely responsible for the attacks, probably carried out by limpet mines, but does not specifically blame Iran.

- Tankers in flames -

In the early hours of June 13, two fuel-loaded tankers passing through the Strait of Hormuz towards the Indian Ocean are hit by mysterious blasts that cause major fires.

One is a Norwegian vessel and the other is Japanese-owned. Their crews are rescued.

The strait is a vital corridor connecting the petroleum-rich states of the Middle East with markets around the world.

Washington, London and Riyadh accuse Tehran of being behind the attacks, which it denies.

- Rocket attacks on Iraq -

On June 18, rockets strike an oil field in Iraq's Basra region, near a camp used by a company of US industrial conglomerate General Electric.

It is the latest in a nearly week-long barrage of anonymous shelling attacks on American interests across Iraq.

The incidents are not claimed but largely originate from areas where Shiite-dominated armed groups loyal to Tehran have free rein.

- US drone downed -

On June 20, Iran's Revolutionary Guards say they shot down a US drone which violated Iranian airspace.

The Pentagon says the drone was in international airspace and denounces an "unprovoked attack".

Trump says he approved a retaliatory strike the next day but cancelled it at the last minute.

On June 24, he announces "hard-hitting" financial sanctions on Iran's supreme leader Ayatollah Ali Khamenei and senior Iranian military leaders.

- Tankers seized and searched -

On July 11, Britain says three Iranian military vessels had tried the previous day to "impede the passage" of a UK oil tanker in Gulf waters but were warned off by a British warship.

Iran's Revolutionary Guards deny there was any confrontation but warn that US and Britain will "strongly regret" the seizure in early July of a tanker off Gibraltar, a British overseas territory in the Mediterranean.

On July 18 Iran's Guards say they have detained a "foreign tanker" and its crew for allegedly smuggling fuel.

The tanker was seized south of the Iranian island of Larak, according to the Guards, who did not detail the name or provenance of the vessel.

- US shoots down Iranian drone -

On July 18, the US military shoots down an Iranian drone that comes within 1,000 yards of one of its naval vessels in the Strait of Hormuz, President Donald Trump says.

The USS Boxer "took defensive action" against the Iranian drone as it was "threatening the safety of the ship and the ship's crew," Trump announced at the White House.

"The drone was immediately destroyed," he added.

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