U.S. President Donald Trump issued another warning to North Korea on Friday, with a reference to American weapons as being "locked and loaded."

"Military solutions are now fully in place, locked and loaded, should North Korea act unwisely. Hopefully Kim Jong Un will find another path!" Trump tweeted a day after his defence secretary said the United States was ready to counter any threat from Pyongyang.

Friday afternoon in Bedminster, N.J., he told reporters, "I hope they will understand the gravity of what I said, and what I said is what I mean."

Asked what he would say to his critics who argue his fiery rhetoric isn't helping the situation, Trump responded, "It's only because it's me. If it was other people, they would say it's a great statement."

Although he didn't use his name, Trump said if North Korean leader Kim Jong-un, "utters one threat in the form of an overt threat, which he has been uttering for years, and his family, or does anything with respect to Guam, or any place else that's an American territory or American ally, he will truly regret it and he will regret it fast."

The remarks aimed at North Korea's leader were the latest in an escalating war of words between Washington and Pyongyang, which, following its latest series of missile and nuclear weapon tests, recently threatened to strike the U.S. territory of Guam. North Korea has said plans to attack the western Pacific island, which is home to about 162,000 people and a major U.S. air force base, could be in place by mid-month.

Trump earlier this week threatened the isolated state with "fire and fury," later adding that that remark might not have been "tough enough."

Meanwhile, South Korea and the U.S. are proceeding with plans for a large-scale military exercise, expected to run from Aug. 21 to 31. The drills will involve tens of thousands of troops on the ground and in the sea and air. Washington and Seoul say they're meant as a deterrent against North Korean aggression.

While tensions typically spike around the dates of the exercises — North Korea conducted its fifth nuclear test just days after last year's manoeuvres — the situation generally calms afterward as the North needs to focus on its farms and the approach of the fall harvest.

The heightened military activity on the peninsula this time is a concern because it could increase the possibility of a mishap or an overreaction of some sort by either side that could spin into a more serious escalation. North Korea has been increasingly sensitive to the exercises lately because they reportedly include training for "decapitation strikes" to kill Kim Jong-un and his top lieutenants.

Earlier on Friday, China's Foreign Ministry called on all sides to speak and act with caution. Beijing hopes all sides can do more to help ease the present tense situation and increase mutual trust, rather than taking turns in shows of strength, the ministry said in a short statement on its website.

Trump has repeatedly called on China — the North's biggest ally and trading partner — to help rein in its neighbour, to little avail. Beijing has expressed frustration with both Pyongyang's repeated weapons tests and with behaviour, such as the military drills, by the South and the U.S.

German Chancellor Angela Merkel and Russia's Foreign Minister Sergei Lavrov also expressed concern, separately, about the escalating rhetoric.

"I see the need for enduring work at the UN Security Council ... as well as tight co-operation between the countries involved, especially the U.S. and China," Merkel told reporters in Berlin.