Seoul, South Korea -- South Korea's military said Thursday that North Korea fired projectiles from the western part of the country into the sea. The U.S. tracked three short-range ballistic missiles, CBS News national security correspondent David Martin reported.

It marked the second North Korea launch in just five days. The North fired several projectiles from its eastern coast on Saturday, and the initial U.S. assessment was that those projectiles were also short-range missiles, Martin reported.

The new launches came amid deadlocked diplomacy between North Korea and the United States aimed at -- from the U.S. side at least -- ridding the North of its nuclear arsenal. They were also carried out during a visit to South Korea by the Trump administration's Special Representative for North Korea, Stephen Biegun, who was meeting South Korean officials in Seoul, "to discuss efforts to advance the final, fully verified denuclearization of North Korea," according to the State Department.

Both the weekend launches and the rockets fired on Thursday would leave the Kim regime just within the confines of the framework of the stalled talks with the U.S., notes CBS News' Pamela Falk at the United Nations, as Mr. Trump has only stressed the need for Kim to abstain from longer-range ballistic missile launches or nuclear tests in his discussions with Kim.

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Thursday's launches came hours after the North, through its state media, described its weekend firing of rocket artillery as a regular and defensive military exercise, and ridiculed South Korea for criticizing the launches.

There was no doubt the first launch was a message. CBS News senior foreign correspondent Elizabeth Palmer said it wasn't completely clear who the message was aimed at, but she said the Kim regime might have be signaling its frustration with the U.S. over the stalled negotiations, after talks between President Trump and North Korean leader Kim Jong Un ended in a stalemate in February.

On Thursday, Palmer said the new launches were a clear message that Kim was indeed growing impatient, and wanted to increase the pressure on the Trump administration to ease its demands in the negotiations.

South Korean President Moon Jae-in appeared to agree, saying after Thursday's launch that "North Korea seemed to be discontented it could not reach a deal in Hanoi."

The Kim regime, noted Palmer, has said the White House has until the end of 2019 to agree the basic terms of denuclearization, or it could walk definitively away from the negotiating table.

Mr. Trump tweeted on Saturday about Kim, but he didn't mention the weekend missile tests.

"Anything in this very interesting world is possible, but I believe that Kim Jong Un fully realizes the great economic potential of North Korea, & will do nothing to interfere or end it," he tweeted. "He also knows that I am with him & does not want to break his promise to me. Deal will happen!"

North Korea's leader Kim Jong Un supervises a "strike drill" for multiple launchers and tactical guided weapon into the East Sea during a military drill in North Korea, in this May 4, 2019 photo supplied by the Korean Central News Agency (KCNA). KCNA/REUTERS

Falk noted that while Mr. Trump has floated the prospect of a third summit with Kim, the talks have been stalled since the North Korean leader appeared to demand the lifting of U.N. sanctions before any further steps toward denuclearization would be taken.