A British man is one of the 24 crew aboard the Danish cargo ship which was seized by Iranian authorities yesterday. He has not been named.
The ship, the Maersk Tigris, was in international waters crossing the Straight of Hormuz from Saudi Arabia to the UAE when it was held by Iranian patrol boats.
A spokesman for Maersk said that they understood that the crew, which is mostly made up of eastern Europeans and Asians is "safe and under the circumstances in good spirits".
A statement added: "We are not able at this point to establish or confirm the reason behind the seizure."
Previously the Pentagon said that the Iranians had fired warning shots across the bridge of the vessel, which is said to be carrying "general cargo", boarded it, and directed it towards the Iranian mainland.
Iran will only agree to a final nuclear accord with six major powers if all sanctions imposed on the country over its disputed nuclear work are lifted, President Hassan Rouhani has said in a televised speech.
"We will not sign any deal unless all sanctions are lifted on the same day... We want a win-win deal for all parties involved in the nuclear talks," Rouhani said.
White House officials have said that US President Barack Obama spoke with the leaders of Bahrain, Kuwait, Qatar and the United Arab Emirates to share details on the framework agreement reached with Iran.
Obama also invited the leaders of the Gulf Cooperation Council to meet with him at Camp David this spring to discuss the tentative deal.
Iran's President Hassan Rouhani has said the agreement on a framework for a deal on Iran's nuclear programme is something that "will go down in the historic memory of the Iranian people".
Speaking on live TV after agreeing preliminary terms with the EU and US, Rouhani also pledged commitment to sticking to the agreement and stated "if we've given a promise ... we will take action based on that promise. Of course, that depends on the other side taking action on their promises too."
Under the terms of the preliminary agreement Iran will continue to enrich uranium at one of its nuclear sites, but will cease operations at a second.
David Cameron has welcomed what he called the "strong deal" achieved in talks over Iran's nuclear programme, claiming that it "has the potential to make our world safer".
The Prime Minister told ITV News' James Mates: "We now need to hammer out the details but at the heart what it says is that Iran's pathways to a nuclear weapon have been blocked off.
"There is proper inspection so that they can't go back on their word, and this has the potential to make our world safer, so we have seen an important breakthrough."
He added: "Crucially, the sanctions - which have done so much to bring Iran to the table - they don't come off unless Iran implements its side of the deal.
Prime Minister Benjamin Netanyahu was set to convene senior ministers on to discuss the framework deal reached between world powers and Iran, which he told US President Barack Obama Israel "vehemently opposed."
The White House said Obama called Netanyahu to discuss the agreement reached with Iran to limit its nuclear programme, saying it represents significant progress toward a lasting solution that cuts off all Iran's pathways to a nuclear weapon.
But Netanyahu said in a statement after the conversation: "A deal that is based on this framework will threaten Israel's existence... The alternative is to stand firmly and increase pressure on Iran until a better deal is reached."
Foreign Secretary Philip Hammond has said that Iran and the six world powers involved in the nuclear talks have established "red lines" within which a deal has been brokered.
Of course there will be people who will try to disrupt this process. Of course there will be naysayers out there, who even before they see the detail will be saying this deal is not good enough.
We know where our red lines are. We have stuck rigidly to our red lines and we've worked out with our Iranian colleagues how we can deliver within the red lines that they have and the red lines that we have.
After delays and missed deadlines, Iran and six world powers have finally reached the outline of an agreement on reining in Iran's nuclear development programme, for the next ten years. President Obama welcomed the breakthrough.
US President Barack Obama has welcomed a preliminary agreement with Iran over its nuclear programme, saying: "It is a good deal."
In a speech after leaders shook hands on solutions for a comprehensive agreement, set to follow in June, Obama said it meant Iran would not develop weapons-grade plutonium, shutting down the potential path to a bomb using enriched uranium.
An intensive inspections deal is part of the plan - and if Iran complies, the international community will begin to phase out sanctions on the country, he added.
Iran will continue to enrich uranium at one of its nuclear sites, but will cease operations at a second, under the terms of a preliminary agreement with the EU and the US.
After lengthy talks, Iran agreed solutions on key parameters of a future comprehensive agreement on its nuclear programme, which is set to be agreed by June 30.
Iranian foreign minister Mohammad Javad Zarif said they were "still some time away" from reaching their desired point, and said Iran would continue enriching uranium at its Natanz site, but not at Fordow.
Leaders also agreed to reduce the current stockpile of around 10,000kg of low-enriched uranium to 300kg for 15 years.
All UN security council resolutions would be included in the comprehensive deal, he added.