South Korea's spy agency told lawmakers that the number of North Korean cyberattacks has doubled over the past month.

Lawmaker Joo Ho-young says the National Intelligence Service gave the assessment to a closed-door parliamentary committee meeting Friday.

Joo's office cited the NIS as saying North Korea unsuccessfully attempted to hack into the railway control system and computer networks of financial institutions in South Korea.

The NIS also accused North Korea of hacking into the smartphones of 40 foreign affairs and military officials in South Korea and stealing their text and voice messages.

Seoul has accused Pyongyang of launching other similar cyberattacks in recent years. Pyongyang has denied the allegations.

Tensions have increased since the North's nuclear test and rocket launch earlier this year and the introduction of further sanctions.