Theresa May will say she is "clear-eyed" about the threat posed by Iran to the security of the Gulf and Middle East, in a speech in Bahrain.

The prime minister will stress the importance of the deal struck last year which "neutralised" the possibility of the country acquiring nuclear weapons.

But she will add that the UK will work with Gulf states to counteract Iran's "aggressive regional actions".

US President-elect Donald Trump has threatened to scrap the nuclear deal.

Signed by Iran and the P5+1 group of world powers - the US, UK, France, China and Russia plus Germany - the deal lifted crippling economic sanctions, after the International Atomic Energy Agency certified that Iran had restricted its sensitive nuclear activities.

Speaking at the Gulf Co-operation Council, Mrs May will recommend ongoing vigilance towards Iran, saying: "As we address new threats to our security, so we must also continue to confront state actors whose influence fuels instability in the region.

"So I want to assure you that I am clear-eyed about the threat that Iran poses to the Gulf and the wider Middle East; and the UK is fully committed to our strategic partnership with the Gulf and working with you to counter that threat."

She will argue that Iran's activities include:

Sending fighters including the Islamic Revolutionary Guards Corps Qods Force to Syria to shore up the Assad regime
Providing support to the Houthis in Sanaa, and so working against the interests of the international community in bringing about peace and stability in Yemen

Undermining stability in Lebanon and Iraq

Mrs May will add: "We secured a deal which has neutralised the possibility of Iran acquiring nuclear weapons for over a decade. It has already seen Iran remove 13,000 centrifuges together with associated infrastructure and eliminate its stock of 20%-enriched uranium.

"That was vitally important for regional security. But we must also work together to push back against Iran's aggressive regional actions, whether in Lebanon, Iraq, Yemen, Syria or in the Gulf itself."

The prime minister will also lead the discussion on Iran, in a session on regional security issues following her speech.

The nuclear deal with Iran followed 12 years of on-off negotiations. It stipulated that Iran will reduce its stockpile of enriched uranium - used to make reactor fuel, but also nuclear weapons - by 98% to 300kg (660lb) for 15 years.

Iran says it does not want a nuclear bomb, but insists on exercising its right to run a peaceful nuclear industry.