The US is monitoring North Korean missile activity

After US Defense Secretary Ash Carter mentioned the possible deployment of America's most advanced missile-defense system to South Korea, the State Department reported on Thursday that it was monitoring North Korean missile activity.

The US is aware of reports that North Korea is preparing intermediate-range missiles and is closely monitoring the Korean Peninsula.

"We call again on North Korea to refrain from actions that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments and obligations," a State Department representative said.

South Korea's Yonhap news agency reported that North Korea has deployed one or two intermediate-range ballistic missiles on the east coast, possibly preparing for launch on or around Friday.

Deployment of a new US missile-defense system to South Korea "is going to happen," US Defense Secretary Ash Carter said on Friday, adding that China should do more to counter North Korea's missile development rather than complain about US plans.

The United States and South Korea began talks on possible deployment of the Terminal High Altitude Area Defense (THAAD) system after the rogue regime's long-range-rocket launch and January's purported hydrogen-bomb test.

Negotiations to equip South Korea with THAAD have been ongoing since South Korean President Park Geun-hye's October 2015 visit to the White House.

As of yet, there has not been a formal move to deploy the missile system.

"The complexity of global-security challenges is increasingly causing combatant commanders to request more Army forces," US Army Capt. Gus Cunningham told Business Insider.

"With that said, THAAD is ready to respond to any request, at any time," Cunningham added.

Reuters contributed to this report.