South Korea warned North Korea Monday that Pyongyang would face a "pitiless penalty" after it blamed the Communist nation for laying two land mines that maimed two South Korean soldiers last week.

The mines exploded Aug. 4 in the Seoul-controlled southern part of the heavily-fortified Demilitarized Zone (DMZ). The two wounded soldiers had been on a routine patrol at the time. One of the injured lost both legs, while the second lost one leg.

South Korea restarted propaganda broadcasts across the border for the first time in 11 years Monday in retaliation for the mine incident.

Monday’s loudspeaker broadcasts were in the western and center portions of the world's most heavily armed border, said Defense Ministry spokesman Kim Min-seok. He said the broadcasts emphasized that the mine explosions were a provocation by the North.

In the past, propaganda broadcasts typically blared messages about alleged North Korean government mismanagement, human rights conditions, the superiority of South Korean-style democracy as well as world news and weather forecasts.

The broadcasts will further test tensions between the Koreas and likely infuriate the North, which is extremely sensitive to any outside criticism of the authoritarian leadership of Kim Jong Un.

It was unclear how long the broadcasts will continue. South Korean officials said they may take additional punitive measures depending on how North Korea reacts.

South Korea's Defense Ministry said Monday that it believes North Korean soldiers secretly crossed the border and laid the mines because the splinters from the explosions were from wood box mines, which are used by North Korea. South Korean authorities claimed that the mines were laid around a door on the South Korean side of the border that opened onto the DMZ.

South Korea's Joint Chiefs of Staff issued a statement urging North Korea to apologize and punish those responsible for the mine explosion. There was no immediate official response from Pyongyang.

The U.S.-led U.N. Command conducted an investigation that blamed North Korea for the mines. It condemned what it called violations of the armistice that ended fighting in the war, which still technically continues because the participants have never signed a peace treaty.

South Korea's Yonhap News Agency reported that South Korean investigators had determined that the explosion was intended to undermine joint military exercises by U.S. and South Korean troops scheduled to take place next week.

More than a million mines are believed to be buried inside the DMZ, and North Korean mines have occasionally washed down a swollen river into the South, killing or injuring civilians. But North Korean soldiers crossing the border and planting mines is highly unusual.

The explosions come amid continuing bad feelings between the rival Koreas over the establishment of a U.N. office in Seoul tasked with investigating the North's human rights record. North Korea also refuses to release several South Koreans it has detained. Things are expected to get worse next week when Seoul and Washington launch annual summertime military drills, which the allies say are routine but North Korea calls an invasion rehearsal.

In 2004, the two Koreas stopped the decades- long practice of propaganda warfare along the border to reduce tension. The practice had included loudspeaker and radio broadcasts, billboards and leaflets. In 2010, South Korea restarted radio broadcasts and restored 11 loudspeakers as part of punitive measures taken after a warship sinking blamed on North Korea that killed 46 South Korean sailors earlier that year. But South Korea didn't go ahead with plans to resume loudspeaker broadcasts at the time.

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The Associated Press contributed to this report.