A timeline of escalation in the Gulf

As tensions escalate in recent months amid a deepening standoff between Iran and the US

DUBAI: Tensions in the Gulf have escalated in recent months amid a deepening standoff between Iran and United States over Tehran's nuclear programme, with a string of incidents involving tankers and drones.

Here is a recap:

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.

The USS Arlington (pictured May 2018), which transports marines, amphibious vehicles, conventional landing craft and rotary aircraft, will head toward the Gulf after intelligence reports suggested Iran was planning some sort of attack in the region. PHOTO: AFP

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

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

On May 8, Iran announces it will drop certain commitments under the agreement, including increasing enriched uranium and heavy water production.

US war against Iran would not last very long: Trump

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

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 tankers suffered "significant damage" but no casualties or oil spill.

Saudi Arabia said two of its oil tankers, including the Al-Marzoqah pictured here, suffered significant damage in sabotage attacks. PHOTO: AFP

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 using limpet mines, but does not specifically blame Iran.

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.

'Alarming accusations': Iran says Trump trying to scapegoat Tehran over tanker attacks

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 armed groups loyal to Tehran have free rein.

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 against Iran's supreme leader Ayatollah Ali Khamenei and senior Iranian military leaders.

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.

A British Royal Navy ship (back R) patrols near supertanker Grace 1 suspected of carrying crude oil to Syria in violation of EU sanctions after it was detained off the coast of Gibraltar on July 4, 2019. PHOTO: AFP

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.

Iran Guards say they have seized a 'foreign tanker'

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 do not detail the name or provenance of the vessel.

On July 18, Trump says the US military has taken down an Iranian drone that came within 1,000 yards of one of its naval vessels in the Strait of Hormuz.

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 says.

The USS Boxer "took defensive action" against the Iranian drone, President Trump said. PHOTO: AFP

Iran denies the claim and suggests American forces may have shot down their own drone by mistake.

On July 19, Iran's Guards seize British-flagged tanker Stena Impero in the Strait of Hormuz for "failing to respect international maritime rules".

This handout photo made available on July 20, 2019, by Jan Verhoog shows the Stena Impero, a British-flagged tanker, off the coast of Europoort in Rotterdam on April 3, 2018. PHOTO: AFP

Following the seizure, UK Foreign Secretary Jeremy Hunt warns of "serious consequences" unless the situation is resolved.

Tehran's arch-foe Saudi Arabia announces that it will host US troops on its soil in a joint move with Washington to "preserve the security of the region and its stability".

Saudi Arabia has not hosted US forces since 2003, when they withdrew following the toppling of Iraqi dictator Saddam Hussein.