North Korea successfully tested its first intercontinental ballistic missile, or ICBM, this week a feat U.S. President Donald Trump had dismissed as an impossibility shortly before his inauguration in January.

The ICBM, potentially capable of carrying a nuclear bomb to Alaska, has triggered fierce condemnation and stoked renewed fears over North Koreas nuclear aspirations and abilities. Trump vowed to confront Pyongyang very strongly on Thursday.

At an emergency United Nations Security Council meeting held on Wednesday to address the recent launch, U.S. Ambassador to the U.N. Nikki Haley said Washington was still considering its options, including the use of military force against the hermit nation.

North Korea has spent years working to develop its highly secretive weapons program , with the goal of creating a nuclear-tipped missile capable of reaching the continental U.S. Experts can only estimate just how long this might take, but they agree that Tuesdays ICBM launch is sounding an alarm over a threat that has been a long time coming.