WASHINGTON, Nov. 23 (Xinhua) -- U.S. President Barack Obama and his South Korean counterpart Lee Myung-bak agreed Tuesday evening to hold more joint military exercises soon as a response to the trade of artillery shelling between Seoul and Pyongyang.

Yonhap news agency reported that both sides have decided to hold the joint naval military exercises on Sunday.

In a telephone conversation, "the two presidents agreed to hold combined military exercises and enhanced training in the days ahead to continue the close security cooperation between our two countries, and to underscore the strength of our alliance and commitment to peace and security in the region," the White House said.

The move came after South Korea and the Democratic People's Republic of Korea (DPRK) on Tuesday exchanged fires in waters off the west coast of the Korean Peninsula.

Obama told Lee that the United States stands "shoulder to shoulder" with South Korea, a close friend and ally of the United States.

The White House said "the United States remains firmly and fully committed to the defense of its ally the Republic of Korea."

Though Seoul blamed Pyongyang for military provocations, there is still no way to confirm who started the shelling attack.

A statement issued by the DPRK army accused South Korea of setting off the exchange of fire, saying dozens of shells from the south fell in the waters of DPRK around Yonphyong Islet at 1:00 o'clock p.m. local time Tuesday afternoon. Ensuing shellings were countering measures of the DPRK, it said.

Acknowledging it did fire shots in the area, South Korea denied any of the test shots fell in the DPRK territory.

The incident came as South Korea was engaged in a massive annual military exercises involving some 70,000 troops, launched Monday and scheduled to last through Nov. 30. Pyongyang has repeatedly warned against such military drills, usually joined by U.S. soldiers, describing them as provocations and real threats to its security.