An unidentified state actor has been blamed for attacks on four oil tankers in the Gulf last month, according to an inconclusive inquiry that stopped short of explicitly pointing the finger at Iran.

The UAE along with Saudi Arabia and Norway presented the preliminary findings during a private briefing to members of the UN security council, which will also receive the final results of the inquiry and consider a possible response.

The US has accused Iran of almost certainly being behind the attacks on the four oil tankers off the Emirati coast, but the brief report, while providing evidence of the sophistication of the attack, goes nowhere near identifying the culprit. Nonetheless, Saudi Arabia today alsoblamed Tehran, its arch rival.

The UAE may be waiting to see whether other intelligence agencies can provide evidence that Iran directed surrogate groups, or possibly Houthi rebels, to carry out the attack.

The four vessels – two Saudi-flagged, a Norwegian-flagged and an Emirati-flagged – were damaged by explosions in UAE territorial waters, off the port of Fujairah.

The UAE is convinced Iran was behind the attacks and that they were designed to send a clear message to the US and the Gulf states about its capacity to wreak havoc on oil shipping, including through the Strait of Hormuz.

Facebook Twitter Pinterest Part of the damaged Saudi-owned oil tanker Amjad off the coast of Fujairah in the UAE. Photograph: Handout/AP

Iran is battling the effects of US sanctions, including on its ability to export oil, the lifeblood of its economy.

The initial findings showed it was “highly likely” that four limpet mines, which are magnetically attached to a ship’s hull under the waterline, were used in the attacks. The report said they had been placed by trained divers deployed from fast boats. The mines were placed soon after the ships were anchored.

The UAE believes the attacks required high-level intelligence in order to identify the four oil tankers as targets, one of which – a Saudi ship – was at the opposite end of the anchorage area at Fujairah from the three other tankers.

The report also said that detailed knowledge of the ships’ designs was required to detonate the mines without sinking the tankers. The mines were sequenced to explode within an hour of each other.

Despite the ambiguous findings, Saudi Arabia continued to blame its arch-enemy, Iran. Tehran has denied involvement.

“We believe the responsibility for this attack lies on the shoulders of Iran,” Saudi Arabia’s UN ambassador, Abdallah al-Mouallimi, said after the briefing. Saudi Arabia maintains that the attacks affect the safety of international navigation and the security of world oil supplies, requiring a response from the security council.

Russia’s deputy ambassador to the UN, Vladimir Safronkov, said after the closed-door briefing that no evidence had been presented linking Iran to the attacks. “We shouldn’t jump to conclusions,” Safronkov said. “This investigation will be continued.”

Tehran reacted coolly to the findings, saying the UAE was determined to blame it as part of an effort to escalate the situation and press the US into a war with Iran.

In an attempt to calm tensions the Japanese prime minister, Shinzo Abe, is due to visit Tehran next week as a mediator between the US and Iran. The German foreign minister, Heiko Maas, is also due to visit Tehran before Abe’s trip.

Germany remains a signatory to the nuclear deal signed in 2015 from which Donald Trump withdrew in May 2018.

Trump then pursued a policy of strong economic sanctions against Iran but he has dialled down his bellicose rhetoric in the last week, waiting to see if any of the mediators can find a basis for setting up direct talks between him and Hassan Rouhani, the Iranian president. Iran will demand the lifting of economic sanctions as a precondition of talks.

On Friday Tehran again ruled out extending the nuclear deal to cover Iran’s ballistic missile programme, something the French president, Emmanuel Macron, suggested should be addressed this week.

France, Germany and the UK have stood by the nuclear deal but have largely failed to find a financial mechanism that protects European companies from the threat of US sanctions if they trade with Tehran. Iran’s oil exports have plummeted and there is a lively debate in Tehran on whether it is tenable to hold out against talks.

Iran is due to show reporters around its heavy water reactor in an attempt to show the implications of the measures it is taking to increase the level of enriched uranium. In response to the US economic pressure, Tehran says it is taking steps to extricate itself from the deal, with the next steps on uranium enrichment due in 30 days.

Germany and Japan are certain to urge Iran to hold back from taking any steps that could be interpreted as abandoning the deal.

Speaking at a conference in Bratislava, Anwar Gargash, the UAE’s foreign affairs minister, said the Iran nuclear deal had not delivered “a peaceful and normal Iran”.

He said: “We are faced with escalation in the region and bellicose rhetoric from Iran, which continues to foster and use sectarianism as a means to insert itself into the Arab world.”

The Iran deal, he said, “did not tackle this dangerous ballistic missile programme or Iran’s regional policies, which include interference in Iraq, Syria and Lebanon and support for proxy forces including the terrorist group Hezbollah”.