US President Donald Trump has said he doesn't think North Korea's launches of short-range missiles this week were a breach of trust, although that could happen in the future.

In a phone interview with Politico on Friday, Trump was asked whether he was angry or frustrated by the firings and if he considered them to be a breach of trust between himself and North Korean leader Kim Jong-un.

"No. No. I'm not at all," he said. "They're short-range. They're short-range and I don't consider that a breach of trust at all. And you know, at some point I may. But at this at this point, no. These were short-range missiles and very standard stuff. Very standard."

Trump has touted North Korea's suspension of nuclear and missile tests as one of his greatest accomplishments since he began diplomatic engagement with the regime last year.

North Korea's test-firings of projectiles -- first last Saturday and again on Thursday -- have been seen as a potential setback to Trump.

His second summit with Kim in February in Vietnam ended without a deal due to differences over the scope of North Korea's denuclearization and sanctions relief from the US

And the weapons tests have been interpreted as an expression of Pyongyang's frustration with Washington.

"Actually, some of them weren't even missiles," Trump said.

"Some of the things that they fired, they weren't even missiles. But this is short-range, and I don't consider it a breach of trust. I'll let you know when I do. I mean, it's possible that at some point I will. But right now, not at all."

Meanwhile, the US this week seized a North Korean cargo vessel it accused of shipping coal in violation of US and United Nations sanctions on Pyongyang, indicating it will keep pressure on the regime. (Yonhap)