North Korea threatens to send army into border zone

North Korea's army has warned it is ready to enter the demilitarised zone dividing the two Koreas.
The threat is partly in response to defector groups in the South sending propaganda material north.
Over the weekend, Kim Yo-jong, the sister of North Korean leader Kim Jong-un, said she'd ordered the army to prepare for the step.
And the military now says it is ready to "turn the front line into a fortress and heighten military vigilance".
Tensions between the two countries have been rising for some time over the cross-border leaflets, usually sent via balloons.
South Korea's defence ministry on Tuesday responded to the renewed threats by saying it was working with the US to closely monitor military moves in the North.