Multiple North Korean soldiers 'killed or injured' by exploding landmines inside Demilitarized Zone just hours before Putin's meeting with Kim Jong Un

Multiple North Korean soldiers have been killed or injured inside the Demilitarized Zone as South Korea fired warning shots early Tuesday morning.

The South Korean military said it fired the shots to repel North Korean soldiers  who temporarily crossed the rivals' land border for the second time this month.

An estimated 20 to 30 North Korean soldiers, while engaging in unspecified construction work on the northern side of the border, allegedly crossed the military demarcation line that bisects the countries at around 8.30am local time.

The North Korean soldiers then retreated after the South broadcasted warnings and fired shots, South Korea's Joint Chiefs of Staff said, adding that they did not see any suspicious activity after. 

As they fled, an unspecified number of North Korean soldiers were injured in a landmine explosion, the Yonhap News Agency reports, according to the AFP.

'North Korean military suffers multiple casualties due to a mine explosion during work,' the report said, without giving further details.

The South previously fired warning shots on June 11 after another group of North Korean soldiers briefly crossed the MDL. 

But South Korea's Joint Chiefs of Staff said that Tuesday´s incident occurred in a different area along the central frontline region. 

They said they don't believe the North Korean soldiers intruded the border intentionally and that the North did not return fire.

But they also said the North has been increasing construction activity in frontline border areas, such as installing suspected anti-tank barriers, reinforcing roads and planting land mines.

South Korean officials noted they recently observed several explosions suspected to have been caused by mines in areas where North Korean soldiers were deployed for construction work, but that the activities continued despite an unspecified number of injuries or deaths.

The Joint Chiefs of Staff now anticipates North Korea will continue to expand its border construction activities, which it said could be aimed at making it harder for North Korean civilians or soldiers to escape to the South as Pyongyang´s leadership attempts to strengthen its control over its people.

The border intrusions come as tensions rise between the war-divided rivals, who in recent weeks have engaged in Cold War-style psychological warfare and made it clear they are no longer bound by their landmark military agreement in 2018 to reduce tensions.

The communist country announced in November that it would abandon the terms of the 2018 agreement with Seoul and move more troops and equipment to the border, after South Korea suspended part of the agreement in response to Pyongyang's successful launch of its first military spy satellite.

In more recent weeks, Pyongyang has sent more than 1,200 balloons carrying trash over its southern border in retaliation for South Korean activists sending balloons of humanitarian aid, Stars and Stripes reports.

Tuesday's incident, meanwhile, comes just hours before Russian President Vladimir Putin is expected to visit the communist country.