The United States urged North Korea on Monday to halt provocations after the communist nation carried out yet another round of ballistic missile launches and fired a barrage of rockets and artillery shells this week.

The North launched two ballistic missiles Sunday from the southern city of Kaesong near the border with South Korea. The missiles flew about 500 kilometers across the peninsula and landed in the East Sea, and the launches were seen as a threat that it can hit any targets in the South.

In another threat to the South, the North also fired about 100 rockets and artillery rounds into the East Sea from a location near the inter-Korean border. The firing marked the third time the North carried out such launches in less than a week.

The U.S. Department of Defense confirmed the North's launch of ballistic missiles.

"We can confirm reports that North Korea launched two short-range ballistic missiles on Saturday," a Pentagon official said. "We urge North Korea to refrain from provocative actions that aggravate tensions and instead focus on fulfilling its international obligations and commitments."

The official also said that the U.S. is closely monitoring the situation on the Korean Peninsula, and urged Pyongyang to exercise restraint and take steps to improve its relations with its neighbors.

The State Department also expressed concerns.

"The United States is concerned by reports that North Korea fired multiple suspected rockets and artillery shells into the sea, just one day after yet another reported round of missile launches," a department official said in an emailed statement.

"As we have emphasized, such provocative actions unilaterally heighten tensions in the region, and they will not provide the DPRK (North Korea) with the prosperity and security it claims to seek," the official said on condition of anonymity.

The official said the U.S. remains "steadfast" in its commitment to the defense of its allies and will continue to coordinate closely with South Korea.

Analysts were divided as to why North Korea has been conducting such launches.

Joel Wit, a former State Department official and editor of the 38 North website at Johns Hopkins University, said that it could be part of its strategy to reopen a stalled dialogue with the South.

"They are part of the North's strategy beginning recently to once again reach out to Seoul to resume dialogue while also demonstrating its military capabilities during the run-up to U.S.-ROK (South Korea) military exercises," Wit said in emailed comments to Yonhap News Agency.

"A key indicator as to how far the North may go in stirring up tensions will be its attitude towards the upcoming 2014 Incheon

(Asian) games, conveniently located near disputed areas of the West Sea," he said.

But Bruce Bechtol, an associate professor of political science at Angelo State University in Texas, said that the firings are believed to be aimed simply at testing new weapons, especially a new 300mm multiple rocket launcher system.

"It's very simple. They simply developed a new longer-range multiple rocket launcher system and you have to test it," Bechtol told Yonhap by telephone, adding that the July-August period is also "the summer training cycle" in the North.

"It appears that they're developing a system that they can put on the DMZ," he said. "Right now, they have systems on the DMZ that can target most of Seoul. but if they put this new system on the DMZ, they can target all of Seoul and they can target Osan Air Base, Camp Humphreys, etc."

The new system has a "better guidance system," and can target "specific squadron areas at Osan Air Base or target even specific areas of the base at Yongsan or the ROK military headquarters. So, this is a very important system," he said. (Yonhap)