President Barack Obama “firmly and fully committed to the defense of its ally the Republic of Korea” during a phone call Tuesday evening to South Korean President Lee Myung-bak following North Korea’s attack on the nation, according to the White House press office.

Obama “strongly condemned” the artillery attack Tuesday on the South Korea island of Yeonpyeong that killed two South Koreans, the statement said. He told Lee that North Korea must follow international law and armistice agreements.

He was briefed on the matter Tuesday by National Security Adviser Tom Donilon, Secretary of State Hillary Rodham Clinton, Defense Secretary Robert Gates, U.S. Ambassador to the United Nations Susan Rice, Joint Chiefs of Staff Chairman Adm. Mike Mullen, and Gen. Walter Sharp, the commander of U.S. Forces Korea.

Obama promised Lee to work with the international community to condemn North Korea and secure the region. The presidents plan to hold combined military exercises “in the days ahead … to underscore the strength of our Alliance and commitment to peace and security in the region,” the statement said.