Tensions between the US and Iran continued to escalate on Monday as National Security Advisor John Bolton accused Iran of “nuclear blackmail” after it threatened to break the limit of uranium enrichment. Earlier on Monday, Iran's atomic agency announced that it is <a href="http://Iran says it will break uranium stockpile limit set by nuclear deal">ramping up enrichment of low-grade uranium</a> and will pass the limit it is allowed to stockpile under the nuclear deal in 10 days. Speaking from the White House, Mr Bolton said the Iranian threats amount to “nuclear blackmail" and called for increased international pressure on Iran if it acts on its threat. He reiterated the US's long-standing position that it will not allow Iran to develop nuclear weapons. In a separate interview with the Washington Free Beacon, a conservative political website, Mr Bolton expressed concern over the security situation in the Gulf of Oman. “It's a very precarious situation,” he told the news website. Following attacks on six tankers in the Gulf Oman in the last five weeks, Mr Bolton said the US is “very concerned about the dangers of the Quds Force and Iranian intelligence operatives”. The Quds Force is a unit in Iran's Revolutionary Guards, which the US announced it was to designate a terror organisation in April. US President Donald Trump's administration holds Iran responsible for the attacks, and has upped its military preparedness and presence in the region to deter and counter such threats. Mr Bolton said that Mr Trump would be willing to reach a deal with Iran "assuming they give up nuclear weapons and stop the other malicious activity that they're engaged in”. "That doesn't mean he's compromising his substantive position. It means, as with North Korea, he's prepared to talk about what the future will be once they give up their nuclear and other unacceptable activities."