Former President Barack Obama Barack Hussein ObamaGOP senator blocks Schumer resolution aimed at Biden probe as tensions run high D-Day for Trump: September 29 Obama says making a voting plan is part of 'how to quarantine successfully' MORE warned President Trump as he left office that North Korea would be “the most urgent problem” he would face, the New York Times reported Saturday.

The report details the Obama administration’s efforts to lead a cyber war against North Korea’s missile program, with a number of the country's military rockets later exploding or veering off course into the sea.

The Trump administration has said all options are on the table for countering the nuclear threat, according to the report. Trump has previously said North Korea will not obtain nuclear weapons.

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“North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the U.S. It won't happen!” Trump tweeted in early January.

The Wall Street Journal in November reported that Obama officials had told members of the Trump transition team that North Korea would be the new administration’s number one national security issue.

North Korea said in September that it had conducted a nuclear test. Over the past eight months, Pyongyang has launched three medium-range rockets and has aimed to create an intercontinental ballistic missile.