SEOUL, Nov. 24 (Xinhua) -- South Korean and U.S. forces have raised their surveillance alert level in the wake of exchange of artillery fire between South Korea and the Democratic People's Republic of Korea (DPRK) on Tuesday, the defense ministry in Seoul said Wednesday.

The alert status had been raised to Watchcon-2 from Watchcon-3 Tuesday night, and South Korea and the U.S.-led United Nations Command are looking into whether the DPRK violated an armistice signed at the end of the 1950-53 Korean War, Shin Hyun-don, an official at Seoul's Joint Chiefs of Staff (JCS), told reporters.

The DPRK on Tuesday fired dozens of artillery shells onto a South Korean island near disputed sea border, killing two marines and injuring several soldiers and civilians.

Seoul vowed retaliation in case of further provocation, while Pyongyang claimed Seoul's shells fell in its side of the disputed maritime border before it fired artillery shells. South Korea was engaged in routine military exercises Tuesday, mobilizing some 70, 000 troops.

Meanwhile, South Korea's defense minister Kim Tae-young had a telephone conversation with his U.S. counterpart, Robert Gates, to discuss possible joint response to what they believed were unprovoked attacks by Pyongyang.

Chairman of the JCS Han Min-koo and Gen. Walter Sharp, commander of the U.S. Forces stationed in South Korea, are also in close contact.

South Korea is currently not considering further upgrading the surveillance level, according to the JCS.