SEOUL, South Korea — North Korea launched four ballistic missiles from its long-range rocket launch site on Monday morning, the South Korean military said. The launch prompted South Korean security officials to call for the early deployment of an advanced American missile defense system that has provoked China.

The missiles took off from Tongchang-ri, in northwest North Korea, and flew an average of 620 miles before falling into the sea between North Korea and Japan, said Noh Jae-chon, a South Korean military spokesman. The type of missile fired was not immediately clear, but Mr. Noh said it was unlikely that they were intercontinental ballistic missiles, which the North had recently threatened to test launch.

During a meeting of the National Security Council, Hwang Kyo-ahn, the acting president of South Korea, called for the early deployment of the American missile defense system known as Thaad, or Terminal High-Altitude Area Defense.

The United States and South Korea have agreed to complete the Thaad deployment within the year. They say it is meant to protect South Korea and American military sites there from North Korean missiles. But China says Thaad would undermine its own nuclear deterrent and has hinted at economic retaliation against South Korea.