Trump's remarks came after he held a meeting with top US military leaders yesterday. The meeting was also attended by the President's advisers, including the National Security Adviser H R McMaster, Chief of Staff John Kelly and Defence Secretary Jim Mattis.
"I put my trust in you to execute our mission aggressively and effectively, and you are delivering. We're ridding our world of terrorism and terrorists as much as it can be done," Trump said.
Noting that he wanted to discuss certain critical things with the military, Trump also listed out some of his priorities.
"In North Korea, our goal is denuclearisation. We cannot allow this dictatorship to threaten our nation or our allies with unimaginable loss of life. We will do what we must do to prevent that from happening. It will be done, if necessary - believe me," he said.
The US must not allow Iran to obtain nuclear weapons. The Iranian regime supports terrorism and exports violence, bloodshed and chaos across the Middle East, he alleged, adding that this is why America must put an end to Iran's continued aggression and nuclear ambitions.
"They have not lived up to the spirit of their agreement," he said.
Trump said in Afghanistan he had lifted restrictions and expanded authorities for commanders in the field.
"You know that very well, and everyone in this room is very happy that it's been done finally. We've made more progress in our campaign to defeat ISIS in the last eight months than in many, many previous years, all combined," Trump said.
Earlier, Trump issued a national security memorandum aimed at integration, sharing and use of national security threat actor information to protect Americans.
National security threat actor information comprises identity attributes and associated information about individuals, organisations, groups or networks assessed to be a threat to the safety, security or national interests of the United States, the memorandum said.