(CNN) Iran has released nine of the 12 Indian crew members who were on board a Panamanian-flagged oil tanker it seized after claiming the vessel was carrying 1 million liters of smuggled fuel.

The move comes as Iran granted consular access to 18 Indian crew members of a separate vessel, the seized British-flagged oil tanker Stena Impero.

The nine sailors were released from the vessel M/T RIAH, the Indian Ministry for External Affairs spokesman Raveesh Kumar confirmed in a statement Friday.

"They will be on their way to India soon," Kumar said. "Our mission in Iran has requested the concerned Iranian authorities for the release of remaining crew members."

US intelligence have been investigating what happened to the M/T RIAH.

And last week, Press TV released video purporting to show the tanker with markings saying "RIAH" and "Panama."

US intelligence officials have been investigating what happened to the M/T RIAH. The ship-tracking website Marine Vessel Traffic has not had a current location for the tanker since July 7.

After US intelligence raised fears that the ship had been forced into Iranian waters last weekend, Iran said that it had assisted one vessel suffering a technical glitch.

It remains unclear who owns the ship. While the initial US intelligence suggested that the tanker was UAE-owned, the United Arab Emirates has said that the tanker in question was "neither owned nor operated by the UAE. It does not carry Emirati personnel, and did not emit a distress call," according to state-run WAM.

Consular access

Meanwhile, Iran's Ambassador to the UK, Hamid Baeidinejad, said Thursday that the Indian Embassy in Tehran had been granted consular access to 18 Indian crew members on board the British-flagged oil tanker Stena Impero, seized by Iran in the Strait of Hormuz last week.

"Indian Embassy in Tehran was granted consular access to meet the 18 Indian crew of the detained British ship Stena Impero," Baeidinejad said on Twitter.

"Similar access is underway to other 5 crew from other nationalities. Indian embassy has reported to find the crew being very calm with no sense of panic."

Indian Minister of State for External Affairs, V. Muraleedharan, on Thursday tweeted a picture of Stena Impero's crew, who hail from India, Latvia, the Philippines and Russia.

"Received an update on 'Stena Impero.' Our Embassy availed consular access today evening. All 18 Indian crew members on board are safe and doing fine. Will continue to push for their early release," the tweet said.

Received an update on 'Stena Impero'. Our Embassy availed consular access today evening. All 18 Indian crew members on board are safe and doing fine. Will continue to push for their early release. @narendramodi @PMOIndia @AmitShah @DrSJaishankar @MEAIndia @VMBJP pic.twitter.com/YqtFupLuZA — V. Muraleedharan (@MOS_MEA) July 25, 2019

A spokesperson for Stena Bulk, the company that operates the tanker, said it was in contact with both the UK and Swedish governments and that local staff in the crew's four home countries were "in constant touch with the families" of the crew and will "continue to do everything humanly possible to keep them informed and to support them in every way we can."

The capturing of the tanker marked another escalation in the tense standoff between Iran and Western powers following US President Donald Trump's decision to withdraw from the Iran nuclear deal last year.

The UK was a party to the 2015 agreement that curbed Iran's nuclear program in exchange for sanctions relief. The British government has made attempts to save the deal alongside France and Germany, the two other European signatories.

But following the tanker's capture, the UK warned Iran that it would take "robust" action in response to the incident. Iran's elite Islamic Revolutionary Guard Corps -- whose troops captured the ship -- accused the vessel of "violating international regulations."

The UK denies this and said the Stena Impero was within Omani territorial waters exercising "the lawful right of transit passage in an international strait."

Increase in tensions

The seizure of the Stena Impero came just hours after authorities in Gibraltar agreed to extend the detention of an Iranian oil tanker in its custody for 30 days.

The UK and Gibraltar seized the Iran-flagged tanker Grace 1 in early July. UK authorities alleged the tanker was attempting to transport oil to Syria, a violation of EU sanctions.

On Thursday, Indian External Affairs ministry spokesman Kumar said an Indian delegation had been granted consular access to the 24-member Indian crew.

@HCI_London team met the Indian crew/staff on board VLCC Grace 1 yesterday. Crew's morale is high. Assured all assistance for early release. HCI London will facilitate necessary travel document and related arrangements. @narendramodi @PMOIndia @AmitShah @DrSJaishankar @MEAIndia pic.twitter.com/xEMsJpNeDo — V. Muraleedharan (@MOS_MEA) July 25, 2019

"What we saw was that the crew members were very calm, very composed, and there was no sense of panic. They had been in regular touch with their family members. We had assured them that the government of India will undertake all the necessary steps to ensure their early release and repatriation," Kumar said.

The recent increase in tensions in the Strait of Hormuz could have dire economic and security consequences.

Around 24% of global oil production passes through the narrow passage, and it's the only way to ship oil out of the Persian Gulf. The US Energy Information Administration calls the Strait of Hormuz one of the "world's most important strategic chokepoints by volume of oil transit."