South Korean sources claim there is evidence that North Korea is about to test-fire short and medium-range missiles, a source said. It comes a day after the two rival nations exchanged artillery fire across the border.

"The North is showing signs of deploying a Scud missile near Wonsan and a Rodong missile in the North Pyeongan Province," a government source told the Yonhap news agency, citing data from a radar system that South Korean and US military operate jointly.

"It seems that (the North) is weighing the timing of the firing under its strategic intention to increase military tension on the Korean Peninsula to the highest level," the source noted.

Pyongyang uses missile tests to demonstrate resilience in standoffs with Seoul, for instance during South Korea’s regular and large military drills with US troops.

The North Korean ambassador to China believes tensions on the Korean peninsula are close to war due to continuous S. Korean political and military provocations.

The leader of the Democratic People's Republic of Korea Kim Jong-un has ordered frontline combined forces to enter a state of war from 5:00p.m. (0830 GMT) on Friday, the official KCNA news agency reports.

The order was issued during an emergency meeting of the central military commission of the ruling party, Xinhua reports. The announcement comes after an exchange of fire between the rivals on Thursday.

(URGENT) N. Korea threatens to dispatch war commander to frontline if South continues propaganda broadcasts http://t.co/Kam425yhWZ — Yonhap News Agency (@YonhapNews) August 20, 2015

South Korean military fired dozens of artillery shells across the border on Thursday, the Yonhap news agency reported. The attack came in response to apparent shelling of the southern part of the border area by the North’s military.

"A barrage of supposedly North Korean military shells was detected by (South Korea's) anti-battery radar" at 3:52pm, a ministry official said as cited by the agency.

Earlier the South Korean Defense Ministry said shelling from across the border was detected by counter-battery radar, but that the South didn’t return fire.

READ MORE: N. Korea threatens to ‘invade US’ unless S. Korean military exercises aren’t halted

No casualties or damage on the ground was reported after the alleged shelling from the North. However, South Korea ordered the evacuation of civilians from the border area to the west of the Korean Peninsula, where the incident happened.

According to the KBS broadcaster in South Korea, the North’s shells targeted a military loudspeaker that has been broadcasting anti-Pyongyang propaganda across the border. North Korea has repeatedly demanded the removal of such loudspeakers, calling them provocative.

In the wake of the fire exchange, North Korea reiterated its demands, saying propaganda must cease within 48 hours or military action will ensue, according to the South Korean Defense Ministry.

N. Korea threatens to turn South into 'sea of fire' over propaganda leaflets http://t.co/CamvIl2Vdrpic.twitter.com/8RBVcOg1ZG — RT (@RT_com) August 15, 2015

Relations between North and South Korea are tenser than usual at the moment in the wake of a land mine incident this month. Two South Korean troops were hit by a primitive landmine explosion, with Seoul blaming Pyongyang, an accusation the North denied. Mounting propaganda loudspeakers along the borders was the South’s response to the incident.