Washington – US officials warned on Friday that threats of retaliatory terror attacks are looming over the US and other countries across the world.

Terror group ISIS had been receiving massive blows in Iraq and Syria.

Officials said that ongoing defeat on the battleground had forced many ultra-hardliners who had left for terrorist hotbeds like Syria and Iraq to return home.

The warning follows the weekend terror attacks in London, which were claimed by ISIS group, and comes amid a growing extremist threat in the Philippines.

Secretary of State Rex Tillerson, speaking from Sydney for an annual conference along with US Defense Secretary Jim Mattis, Chairman of the Joint Chiefs of Staff Joseph Dunford and the head of Pacific Command Admiral Harry Harris, said a decision on whether to send additional troops to try to stabilize the security crisis in Afghanistan was still under review.

ISIS militants will “come back with battlefield skills, they’ll come back with hardened ideology, they’ll come back angry, frustrated, and we need to be very aware of that,” Australian Defense Minister Marise Payne said.

Reacting to the London attacks, Defense Secretary Mattis said: “We are united… in our resolve, even against an enemy that thinks by hurting us, they can scare us. Well, we don’t scare.”

US President Donald Trump has instructed the Pentagon to “annihilate” ISIS to try to prevent foreign militants from escaping and returning home as they lose ground in Iraq and Syria.

The aim is to encircle and kill as many extremists as possible in place, rather than letting them exit a city and targeting them as they flee. This reflects an increasing urgent attempt to stop the militants bringing their military expertise and ideology back to the West.

“Before, we were shelling them from one town to another,” Mattis said.

“We now take the time… to make certain that foreign militants do not stay to return to Paris, France, to Australia, to wherever they came from, and bring their message of hatred and their skills back to those places and attack innocent people.”

The issue of countering terrorism was high on the agenda at Monday’s annual talks.

Australian officials say they have prevented 12 terror attacks on home soil since 2014 with more than 60 people charged.