Al-Jazeera - The Trump administration wants a Senate-approved agreement with Iran to replace the 2015 nuclear deal that the US president withdrew from last year, US Special Representative for Iran Brian Hook told Al Jazeera on Tuesday.

According to the Trump administration, one of the major flaws of the deal, which was agreed to under former President Barack Obama, was that it was not formally ratified by the US Senate.

"We want a deal that we're going to submit to the Senate as a treaty that would enjoy not just the support of the president, but the United States," Hook said. "That's going to be a deal that's more than just a political commitment, he added.

But nonproliferation experts say US President Donald Trump would first need to get Iran to negotiating table, which is highly unlikely at this point given that Tehran has repeatedly said it will not engage in talks with the US while sanctions are in place.

"Unless the Trump administration goes back into the Iran deal - which they have said they are not going to do - I don't see any possibility of a new deal," said Tom Z Collina, director of policy for Ploughshares Fund in Washington, DC, a nonproliferation advocacy group.

"Unless the Trump administration does that, Iran has said it's not interested in talking with the United States which has shown itself to be a dishonest and unreliable partner," Collina told Al Jazeera.

Obama, who negotiated the Iran deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), did not have the needed Senate votes for the ratification of the deal as a treaty because of "blanket Republican opposition, despite broad expert opinion that it was a good deal", Collina said.

"If [Trump] gets a deal, and it's a very good deal, I could see Trump getting Republican and Democrat support from two-thirds of the Senate in a way that Obama would have been unable to do," he added.

Military coalition
Hook also told Al Jazeera that Gulf Arab states could be more effective in confronting Iran if they were united.

On Tuesday, the chairman of the US Joint Chiefs of Staff said Washington was working to form a military coalition to protect commercial shipping off the coast of Iran and Yemen amid heightened tensions in the region following attacks on oil tankers in the Gulf.

Under the proposal, a coalition of nations would patrol strategic waters in the Gulf area and the sea between the Arabian Peninsula and the Horn of Africa, Marine General Joseph Dunford said.

"We're engaging now with a number of countries to see if we can put together a coalition that would ensure freedom of navigation both in the Straits of Hormuz and the Bab al-Mandab," Dunford said.

He added that the Pentagon had developed a specific plan, and that he believed it would be clear within a couple of weeks which nations were willing to join the effort.

Mark Esper, the acting US secretary of defence, raised the issue last month with allied officials at NATO headquarters, but no nations were ready to commit to participating. Esper said at the time that the plans would have to be further refined.

Dunford suggested on Tuesday that the project could begin with a small coalition.

"This will be scalable. So, with a small number of contributors, we can have a small mission and we'll expand that as the number of nations that are willing to participate identify themselves," he said.

The Trump administration has blamed Tehran and its proxies for several attacks on tankers in the Gulf in the past few months - allegations Tehran denies.

A fifth of the world's oil exports passes through the area.

Al Jazeera's John Hendren, reporting from Washington, DC, said that Trump has declared that "the US should not pay for this, it should be an international military force".

"But the move presents the potential for conflict with Iran. After all, it's only weeks after the US almost launched military strikes on Iran," Hendren said.

War of words
The downing of a US surveillance drone by Tehran last month almost brought the two foes to the brink of direct military confrontation. Trump had authorised military attacks on Iran in retaliation but pulled back from launching them at the last minute.

At the time, members of the US Congress cautioned Trump against escalating a standoff with Iran, saying any missteps could widen the conflict.

Washington instead slapped new sanctions on top Iranian leaders, including the supreme leader, Ali Hosseini Khamenei.

Tensions between Washington and Tehran have intensified since May 2018, when Trump unilaterally withdrew from a 2015 nuclear deal that put a cap on Tehran's nuclear ambitions in exchange for sanctions relief.

The crisis has escalated in recent days as Washington and Tehran have engaged in a war of words over Iran's decision to pass the uranium enrichment limit set by the 2015 accord.

Trump said on Wednesday that sanctions on Iran "will soon be increased, substantially". He did not offer details.

Iran's ambassador to the International Atomic Energy Agency, which was holding an emergency meeting on Wednesday to discuss Tehran's nuclear programme, responded, saying his country faces "economic terrorism" from the US with its "sadistic" sanctions.

Tehran has asked the other parties to the nuclear deal - France, Britain, China, Russia, the European Union and Germany - to find ways to export its oil, a major source of revenue for its crippled economy that has been choked off by the new sanctions, or it will scale up its nuclear programme.

Trump has said the US will not allow Tehran to acquire nuclear weapons, with its close ally in the region, Israel, threatening to bomb Iran.

"We want to deny this regime the revenue it needs to export revolution, to run an expansionist foreign policy that drives a lot of the sectarian violence that we see in the Middle East," Hook told Al Jazeera.

Iran has previously denied that it is seeking nuclear weapons.