SEOUL (Reuters) - North Korea will take more action to maintain its military power despite U.S. sanctions pressure that has only made the country stronger, a North Korean foreign ministry official said on Thursday.

"U.S. heinous sanctions served as a catalyst and driving force that unleashed a gradual increase in our national strength," state KCNA news agency cited a North Korean senior foreign ministry official as saying, referring to its nuclear tests prompted by international sanctions led by Washington.

The country "will protect its sovereign rights and security interests from increasing hostile threats and sanctions pressure from the United States, and take stronger real actions to make its already established military and technological strength irreversible," the official added.

Kim Yo Jong, the powerful sister of North Korean leader Kim Jong Un, said on Wednesday that the country would press on with its "overwhelming" military buildup in response to frequent U.S. military drills with South Korea.

The U.S. and South Korean militaries have conducted a range of drills with greater scale and intensity in recent months under a pledge by the two countries' leaders to upgrade military readiness against North Korea's military threats.

North Korea says U.S. military exercises are preparations for a nuclear war against it.

"We are used to U.S. sanctions, and we have the ability and great power to stand up to any harsh sanctions," the foreign ministry official said, according to KCNA.

(Reporting by Ju-min Park; Editing by Sonali Paul)