Prime Minister David Cameron has pledged to fully support troops but spoke of "difficult decisions ahead" as he witnessed the passing-out ceremony of officer cadets.
Representing the Queen at the Royal Military Academy Sandhurst, Surrey, he said that the "defence of the realm" is the Government's top priority.
Mr Cameron watched from the royal dais as 226 officer cadets were commissioned in the Sovereign's Parade.
He inspected the troops, stopping to chat to several of the young men and women before addressing them.
Mr Cameron said: "In return for all you will give to your country, I want your country to have pride in you. As a Government we will do everything we can to support you, to look after your families and to rebuild the military covenant that is so important to our country. First and foremost that means supporting you. Yes, there will be difficult decisions ahead but I will never forget that defence of the realm is the first duty of any government."
He spoke of his own personal pride at attending the passing-out parade, witnessed by about 3,000 friends and relatives of the officer cadets, including several heads of state.
Mr Cameron also urged the officer cadets to take pride in their new careers. He said: "I want you to be proud of the difference that you can make. The security of our nation, and that of our allies across the world, is at stake."
The Prime Minister warned that to withdraw troops from Afghanistan now could provide the Taliban with an opportunity to attack the West from there.
He added: "I say we cannot let that happen. But it's what you will do that will actually prevent it. "You will be helping to defend our way of life. And there is no greater calling than that."
Among the dignitaries present was the King of Swaziland, the President of Yemen, the Prime Minister of Bahrain and the Ruler of Umm Al Qaiwain in the United Arab Emirates, all of whom had sons or grandsons passing out. General Mohammed Mangal, deputy minister of Interior of Afghanistan, also attended as two Afghan cadets were passing out.
