Extra money should be spent on the SAS and drones to combat the threat of Islamic State (IS) terrorists, David Cameron has told defence chiefs.
The Prime Minister has asked military top brass and officials to look at increasing funding for special forces and other counter-terror capabilities as part of the Strategic Defence and Security Review (SDSR).
The defence chiefs have also been urged to consider new spy aircraft, including drones, to gather intelligence about IS, also known as Isil, or other terror groups.
The Prime Minister wants the SDSR, due to conclude in the autumn, to prioritise resources that will help to protect the UK from evolving threats - not only terrorism and extremism but also an increasingly aggressive Russia and the risks posed by cyber attacks.
The defence chiefs were told of the Prime Minister's priorities last week in a meeting following the Budget commitment to continue meeting the Nato target of spending 2% of GDP on defence.
Mr Cameron said: "As Prime Minister, I will always put the national security of our country first. That's why it is right that we spend 2% of our GDP on defence because this investment helps to keep us safe. It has only been possible because of the difficult decisions we have made to ensure a strong and secure economy.
"Now we know how much we will spend, what matters next is how we spend it. I have tasked the defence and security chiefs to look specifically at how we do more to counter the threat posed by Isil and Islamist extremism.
"This could include more spy planes, drones and Special Forces. In the last five years, I have seen just how vital these assets are in keeping us safe."
The review will also examine how the Royal Navy can work with partners such as the United States to use the new aircraft carrier HMS Queen Elizabeth to deploy drones and special forces against terrorists.
The vessel is due to enter service in 2020 and Mr Cameron will welcome some of the ship's company to Downing Street today.
The Prime Minister will also visit RAF Waddington, the UK's drone base in Lincolnshire, from where operators fly unmanned aircraft over Iraq and Syria.
The RAF's jets and drones are part of the coalition attacking IS in Iraq, but in Syria the drones are limited to a surveillance role - although ministers have begun setting out the case to extend the bombing campaign to the terror group's strongholds in that country.