WEST POINT, New York - The US Defense Secretary James Mattis said on Saturday that his country is committed to fighting terrorism, as "Americans are not made of cotton candy".

The retired four-star Marine general made the remarks while talking to the 936 graduating cadets at Army 'sfootball stadium of the US Military Academy, located in West Point, about 96 kilometers north of New York City on the Hudson River.

"Manchester's tragic loss underscores the purpose of your years of study and training at this elite school," Mattis said, referring to the May 22 suicide bombing outside the Manchester Arena in England after a concert by US pop singer Ariana Grande. Twenty-two people were killed and more than 100 injured. The Islamic State terrorist group has claimed responsibility for the attack.

British police made two more arrests and stormed three more locations Sunday as they hunted for suspects in the bombing, while a government minister said members of attacker Salman Abedi's network may still be at large.

Greater Manchester Police said two men - one aged 25 and the other 19 - were arrested in the city on suspicion of terrorist offenses. Eleven other men between the ages of 18 and 44 also were in custody.

Most of the searches and arrests since Monday night's bombing have been in multi-ethnic south Manchester, where Abedi - the son of Libyan parents - was born and raised.

"The operation is still at full tilt,"Home Secretary Amber Rudd said, adding that some suspects could remain at large.

British police now have 13 suspects in custody - including Abedi's elder brother Ismail - and have searched properties across Manchester. Another brother and Abedi's father have been detained in Libya.

"We must never permit murderers to define our time or warp our sense of normal. This is not normal," said Mattis, who became defense secretary on Jan 20, hours after Republican President Donald Trump was sworn in.

"You will drive home a salient point," Mattis said. "That free men and women will volunteer to fight, ethically and fiercely, to defend our experiment that you and I call, simply, 'America.'

"We Americans are not made of cotton candy. You are a US soldier and you hold the line," he said to cheering and applause from the graduates. "Our enemies are watching," he said. "By your commitment, you will prove the enemy wrong. Dead wrong."

The US Military Academy, known as West Point, was founded in May 1802. It has an undergraduate enrollment of 4,348. Army graduates earn a bachelor of science degree and almost all of them are commissioned as second lieutenants in the US Army.

Xinhua-AP