efe-epaBy Marina Villén Tehran

The British tanker Stena Impero and its crew remained in Iranian custody near the port city of Bandar Abbas on Sunday amid a deepening diplomatic crisis between London and Tehran, which has warned against escalating tensions.

UK authorities have labeled Iran's seizure of the Stena Impero as "illegal" and the incident sparked alarm in the international community over increasing instability in the Persian Gulf region.

Mohammad Javad Zarif, Iran's foreign minister, blamed the United States National Security Advisor John Bolton for pulling the UK into his plan for war.

"Make no mistake: Having failed to lure Donald Trump in War of the Century, and fearing the collapse of his B team, John Bolton is turning his venom against the UK in hopes of dragging it into a quagmire. Only prudence and foresight can thwart such ploys," he wrote on Twitter.

The crisis between London and Tehran began two weeks ago when UK authorities detained Iranian tanker Grace 1 off the coast of British overseas territory Gibraltar following claims from the US that it was transporting oil to Syria, and thus breaching international sanctions.

The capture of Stena Impero only aggravated things and the UK had warned Iran of "serious consequences."

UK defense minister, Tobias Ellwood, also called for a de-escalation of tensions.

He downplayed accusations that he had "taken his eye off the ball" by not ensuring better protection for the vessel.

The Iranian ambassador to the UK, Hamid Baeidinejad, urged calm but said Iran was prepared for different outcomes.

"UK government should contain those domestic political forces who want to escalate existing tensions between Iran and the UK well beyond the issue of ships. This is quite dangerous and unwise at a sensitive time in the region" he wrote on Twitter.

Iran is unlikely to release the Stena Impero until UK authorities release Grace 1.

According to Iranian maritime authorities, the crew of the Stena Impero are being investigated for allegedly hitting a fishing boat and navigating the wrong waterway in the Strait of Hormuz, the thin channel of water connecting the Persian Gulf and the Gulf Oman that has become a flashpoint in tensions in recent weeks, especially between Iran and the US.

Company Stena Bulk has denied those accusations.

The 23 crew members on board, the majority Indian nationals, were safe and well, according to Iranian authorities.

The Strait of Hormuz is an important waterway in the global oil trade but it has also been the scene of increased hostilities playing out between Tehran and Washington.

The US recently claimed to have shot down an Iranian unmanned drone over the Strait, although Iran denied this.

Last month, Iranian armed forces did shoot down a US surveillance drone.

Washington, meanwhile, has accused Iran and its proxies of a series of sabotage attacks against oil tankers in the region, something Iran denies.

Animosity skyrocketed after Trump withdrew from the 2015 nuclear deal, which sees Tehran trade in much of its nuclear program for a loosening up of sanctions.

Trump proceeded to tighten sanctions on Iran, targeting its oil and banking sectors. EFE-EPA

mv/jt