European leaders on Monday urged the United States to exercise maximum restraint toward Iran and avoid military confrontation as tensions in the Persian Gulf region continue to escalate in the last days.

The warning came after US Secretary of State Mike Pompeo paid a hastily arranged visit to Brussels on Monday and the news that four oil tankers in the Gulf of Oman were allegedly sabotaged on Sunday.

Pompeo met High Representative of the European Union for Foreign Affairs and Security Policy Federica Mogherini and some other foreign ministers of key EU member states.

"Mike Pompeo heard very clearly today from us, not only from myself, but also from other ministers of EU member states that we're living in a crucial, delicate moment where the most relevant attitude to take, the most responsible attitude to take, is and we believe, should be maximum restraint and avoiding any escalation on the military side," Mogherini told a news conference on Monday.

The US has stepped up its military presence in the Persian Gulf, including dispatching aircraft carrier strike group and B-52 bombers. US National Security Adviser John Bolton, a hawk on Iran, said last week that any attack on US or its allies "will be met with unrelenting force".

"I'm hearing little stories about Iran. If they do anything, they will suffer greatly. We'll see what happens with Iran," US President Donald Trump said in Washington on Monday.

Mogherini said the EU is still gathering information and assessing the situation regarding the ship sabotage. "I confirm my worry about the risks of an escalation in a region that definitely doesn't need further elements of destabilization and tensions. Our call is to show maximum restraint from all sides."

Mogherini, a former Italian foreign minister, expressed her hope for Iran to continue to comply with the 2015 landmark nuclear deal reached by Iran, the EU, the US, China, Russia, France, Germany and the United Kingdom. The US withdrew from the agreement last year and reimposed sanctions on Iran, including threat to cut Iran's oil exports to zero.

The International Atomic Energy Agency has confirmed that Iran has lived up to the deal in all its 14 reports. Mogherini said the agency is the only body entitled to verify the issue.

She said that the EU and its member states are fully determined to do all they can and will use all their instruments to implement in full their part of the agreement as long as Iran remains compliant with the nuclear deal.

The first transactions are expected to take place in the next few weeks under the Instrument in Support of Trade and Exchanges, or INSTEX, a special purpose vehicle designed to facilitate trade with Iran without recourse to banks, Mogherini said.

Iran, which has grown increasingly frustrated with the incompetence of the EU and some other signatories to protect its economic interests, announced last week that it was preparing initial steps to distance itself from the nuclear deal.

In Brussels on Monday, British Foreign Secretary Jeremy Hunt, French Foreign Minister Jean-Yves Le Drian and German Foreign Minister Heiko Maas also expressed their concerns over the growing tensions in the region.

Tarja Cronberg, a fellow at the Stockholm International Peace Research Institute, expressed that the US is acting unilaterally and is in breach of UN Security Council resolution 2231 which codified the JCPOA. "Despite US provocations, Iran has so far complied with its obligations under the resolution," he wrote on Monday in an article posted on the Atlantic Council website.

But he noted that it is not possible for the EU to counter the US economically given the dollar's dominance in the world economy. "The EU has not dared to enforce counter-sanctions on US firms nor on those of its allies. INSTEX is as far as the EU would go," wrote Cronberg, former chair of the European Parliament's Iran delegation.

Politico contributed to the story.