A surprise underwater attack by North Korea will not keep South Korea from retaliating against the communist nation.

South Korea held anti-submarine drills Thursday in conjunction with its U.S. allies offering words of support and warning North Korea not to try attacking again.

"We call on North Korea to cease all acts of provocation and to live up with the terms of past agreements, including the armistice agreement," Gen. Walter Sharp said Thursday, during a Memorial Day speech.

However, Pyongyang responded to the exercise, warning it would launch "immediate physical strikes" against ships that enter its territory.

This comes as tensions increased one week after Seoul put the blame on the North for sinking its warship Cheonan in a torpedo attack, casuing the  deaths of 46 sailors.

A fleet of 10 warships, which included a 3,500-ton destroyer, fired artillery and other naval guns and dropped anti-submarine bombs during the one-day exercise.

It was the first drill since the attack on the Cheonan two months ago.

South Korea also plans to have two major military drills with U.S. forces in July, according to South Korea's Joint Chiefs of Staff.