North Korea conducted its second weapons test in less than a week Wednesday, firing two short-range ballistic missiles off its east coast. Observers say the move could be aimed at boosting pressure on the United States as the rivals struggle to set up fresh nuclear talks.

U.S. officials told CBS News the weapons fired Wednesday appeared very similar to ones launched six days ago – which were nuclear-capable and would be difficult for defense systems to track and destroy. The U.S. has had little or no warning of recent North Korean short range tests, a U.S. official told CBS News.

South Korea's Joint Chiefs of Staff said in a statement that the missiles were launched from Wonsan, a city the North pushes as a vacation destination but that it also uses as a regular launch site. It said both missiles were believed to have flown about 155 miles at a maximum altitude of 19 miles and that the South Korean and U.S. militaries were trying to gather more details.

The test was yet another North Korean violation of U.N. Security Council resolutions and comes as the country's negotiations with the U.S. over its nuclear weapons program are at a stalemate and as Pyongyang has expressed anger over planned U.S.-South Korean military drills.

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Last Thursday North Korea fired two short-range missiles in what state-run media called a "solemn warning" to "South Korean military warmongers."

Also last week, Kim visited a newly built submarine and expressed his satisfaction with its weapons system. North Korea said its deployment was "near at hand."

In a private briefing to lawmakers Wednesday, South Korean military intelligence officers said they've determined that the submarine likely has three launch tubes for missiles. If confirmed, it would be North Korea's first operational submarine with missile launch tubes, some experts said.

The United Nations Security Council scheduled a closed-door meeting for Thursday, at the request of Britain, France and Germany, to discuss Pyongyang's recent missile launches.

South Korean officials said last week's launch involved a new type of a short-range ballistic missile. That was the first launch by North Korea since Kim Jong Un and President Trump met at the Demilitarized Zone in June and Mr. Trump took a few historic steps across the border into North Korea. Mr. Trump told Fox News last week that he was "getting along well" with Kim and said the country "really haven't tested missiles other than smaller ones."

Secretary of State Mike Pompeo has said no new high-level talks between U.S. and North Korean officials are currently scheduled.

Both launches were violations of U.N. Security Council resolutions that ban North Korea from engaging in any launch using ballistic technology. While the North could face international condemnation over the latest launches, however, it's unlikely that the nation -- already under 11 rounds of U.N. sanctions -- will be hit with fresh punitive measures. The security council has typically imposed new sanctions only when the North conducts long-range ballistic launches.

North Korea's state media said last week's missile tests, supervised by Kim, were designed to deliver a "solemn warning" to South Korea over its purchase of high-tech U.S.-made fighter jets and its plans to conduct military drills that Pyongyang sees as an invasion rehearsal. The North's state media report avoided a direct criticism of the United States.

South Korea's military said the flight data of the weapon launched last week showed similarities to the Russian-made Iskander, a short-range, nuclear-capable missile. A North Korean version could likely reach all of South Korea -- and the 28,500 U.S. forces stationed there -- and would be extremely hard to intercept.

David Martin and Ramy Inocencio contributed to this report.