The Prime Minister is travelling to the frontline of the war on terror for talks on stepping up the fight against Islamic State, known as Daesh, and tackling the Syrian refugee crisis.
Theresa May is visiting Jordan and Saudi Arabia and will pledge more UK support for airstrikes, new counter-terrorism measures and humanitarian efforts.
First, in Jordan, she will announce a joint anti-terror initiative, with new moves "to strike at the heart of Daesh", and promise to improve co-operation on countering violent extremism in the region.
Then, in Saudi Arabia, the UK's largest trading partner in the Middle East, as well as talks on boosting trade between the two countries she will attempt to step up co-operation on counter-terrorism.
During her visit, the Prime Minister is expected to say that the tragic attack in Westminster on 22 March "showed only too starkly that terrorism is an evil facing us all and we must come together to fight it".
She will also say that working with countries such as Jordan on the frontline in the fight against terror keeps British people safe, and that sharing intelligence with Saudi Arabia has saved hundreds of lives in the UK.
According to 10 Downing Street, she will also discuss how the UK Government can build on co-operation with Jordan to manage the fall-out from the Syrian conflict.
She is expected to reiterate the UK's commitment to providing humanitarian support to Jordan to bolster its capacity to handle the huge number of refugees it hosts, enabling the refugees to stay close to their homes and create meaningful long-term futures for themselves.
The Prime Minister will begin her visit in Jordan's capital, Amman, where she is expected to agree new support for the Royal Jordanian Air Force to improve its capability to strike Daesh targets and defeat the terrorist threat.
She will then visit Saudi Arabia, where - according to No 10 - she will make clear that they are a close and important ally and that the UK will continue to work closely in a range of areas, particularly on counter-terrorism, where UK-Saudi cooperation is vital.
On trade, the Prime Minister is expected to explore ways of boosting already strong ties. Exports of British goods were worth £4.67bn in 2015 and services £1.9bn.
Speaking ahead of her visit, the Prime Minister said: "As the United Kingdom leaves the EU, we are determined to forge a bold, confident future for ourselves in the world.
"We must look at the challenges that we, and future generations, will face and build stronger partnerships with countries that will be vital to both our security and our prosperity.
"It is clearly in the UK's security and prosperity interests to support Jordan and Saudi Arabia in tackling regional challenges to create a more stable region, and in delivering their ambitious reform programmes to ensure their own stability.
"An even deeper partnership with these countries, and greater knowledge and understanding of one another, will increase our ability to address the issues that concern us, including the promotion of international standards and norms.
"To tackle the threats we face from terrorism and from geopolitical instability, we must meet them at their source.
"Jordan is on the frontline of multiple regional crises and I'm clear that by working with them, we are helping keep British people safe.
"Likewise in Saudi Arabia: we must never forget that intelligence we have received in the past from that country has saved potentially hundreds of lives in the UK.
"And there is so much we can do together on trade, with immense potential for Saudi investment to provide a boost to the British economy.
"So I hope my visit will herald a further intensification in relations between our countries and deepen true strategic partnerships, enabling us to seize the opportunities ahead and ensure the security and prosperity of our people for decades to come."
It is not the Prime Minister's first visit to these two key Gulf states. She visited Jordan in 2012 when she was Home Secretary and also visited Saudi Arabia in March 2014.
The UK Government's new support for the Royal Jordanian Air Force will include:
:: Deploying training teams to help the Jordanians better integrate their Air and Land assets on operations;
:: Providing training in the UK and in Jordan for Joint Terminal Attack Controllers, who are the service personnel who direct combat action of aircraft in offensive operations;
:: Increasing the number of places available to RJAF personnel on UK courses in niche areas such as Air Battle Management and Electronic Warfare; and
:: Supporting aviation safety, including through training in both the UK and Jordan.
According to No 10, the UK will also commit to partnering with Jordan in the development and implementation of strategies to counter violent extremism, including active consultation with civil society and affected communities, particularly focusing on youth groups.