SEOUL - North Korea's hacking groups have broken into at least two South Korean manufacturers of chipmaking equipment, as the country looks to evade sanctions and turn out its own semiconductors for weapons programmes, South Korea's spy agency said on Monday.

The news comes after South Korean President Yoon Suk Yeol warned North Korea could stage provocations, such as cyber attacks or spreading fake news, to interfere in April's parliamentary elections.

The National Intelligence Service (NIS) said the South Korean firms had been a key target of North Korean hackers since late last year, and called for tougher security.

North Korea penetrated the servers of two companies in December and February, stealing product design drawings and photographs of their facilities, the NIS said.

"We believe that North Korea might possibly be preparing to produce its own semiconductors in the face of difficulties in procuring them due to sanctions," it said in a statement.

Also driving the North's efforts could be higher demand from its satellite, missile and other weapons programmes, it added.

Pyongyang has always denied involvement in cybercrimes, although North Korea has been blamed for cyberattacks netting millions of dollars.

The hackers employed a technique called "living off the land," which minimises malicious codes and uses existing, legitimate tools installed within the servers, making it difficult to detect with security software, the NIS said.

(Reporting by Hyonhee Shin; Editing by Clarence Fernandez)