South Korean and U.S. forces engaged Tuesday in non-proliferation maritime interdiction exercises in the Yellow Sea as they entered the third day of the latest joint maneuver.

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The drills, aimed at preventing the spread of weapons of mass destruction under a U.S.-led campaign, came as part of the four-day joint show of force against Pyongyang, though Seoul and Washington have stressed their "defensive" nature.

The allies, apart from conducting a mock inspection of ships suspected of carrying weapons of mass destruction, also held air defensive exercises using radar systems from Aegis destroyers, according to the Yonhap News Agency.

The massive joint exercises, though originally planned well before the DPRK's artillery shelling of a South Korean border island last Tuesday, come amid the mounting military tensions on the divided peninsula following the exchange of fire that killed two South Korean marines and two civilians.

Seoul and Washington denounced the artillery bombardment as an "unprovoked attack" that targeted South Korean soil and civilians for the first time since the 1950-53 Korean War ended with a truce, not a formal peace treaty.

Pyongyang, claiming the attack for "self defense" was provoked by the South Korean and U.S. forces then engaged in an annual naval exercise near a disputed western sea border, repeatedly warned of a strike against the ongoing war games by Seoul and Washington.