On 13 April 2017, NBC reported that the United States is “prepared” to launch a preemptive strike against North Korea to prevent it from testing another missile:

The U.S. is prepared to launch a preemptive strike with conventional weapons against North Korea should officials become convinced that North Korea is about to follow through with a nuclear weapons test, multiple senior U.S. intelligence officials told NBC News.

North Korea has warned that a “big event” is near, and U.S. officials say signs point to a nuclear test that could come as early as this weekend.

The intelligence officials told NBC News that the U.S. has positioned two destroyers capable of shooting Tomahawk cruise missiles in the region, one just 300 miles from the North Korean nuclear test site.

American heavy bombers are also positioned in Guam to attack North Korea should it be necessary, and earlier this week, the Pentagon announced that the USS Carl Vinson aircraft carrier strike group was being diverted to the area.

In an e-mail, a Defense Department spokesperson would not confirm that was the case but did say that the United States military is ready for any scenario. Marine Corps Maj. Adrian J.T. Rankine-Galloway wrote:

For security reasons, we do not discuss future operations nor publicly speculate on possible scenarios. Commanders are always considering a full range of options to protect against any contingencies. Our commitment to the defense of our allies, including the Republic of Korea and Japan, in the face of potential threats, remains steadfast.

Tensions have reached a high on the Korean peninsula, particularly after North Korea on 5 April 2017 launched its fifth missile test. The projectile landed in the Sea of Japan. Per Reuters:

The North is believed to be developing an intercontinental ballistic missile (ICBM) that could hit the United States, and its leader, Kim Jong Un, has vowed to test-launch one at any time.

Experts and officials in the South and the United States believe Pyongyang is still some time away from mastering all the technology needed for an operational ICBM system, such as re-entry into the atmosphere and subsequent missile guidance.

In response to the most recent missile test, the U.S. routed a naval strike group to the Korean peninsula as a show of force. North Korea’s main ally China has discouraged military aggression and urged diplomacy to solve the issue, but U.S. President Donald Trump has said the U.S. would “deal” with Pyongyang without China if necessary.

Sources:

Arkin, William M., et al. “U.S. May Launch Strike if North Korea Reaches For Nuclear Trigger.”
  NBC News. 13 March 2017.

Park, Ju-min, and Kim, Jack. “North Korea Test-Fires Missile Into Sea Ahead of Trump-Xi Summit.”
  Reuters. 5 April 2017.

Martina, Michael, and Wong, Sue-Lin. China warns against force as North Korea prepares celebration
  Reuters. 13 April 2017.