 -- Ahead of Vice President Mike Pence's trip to neighboring South Korea this weekend, tensions between the United States and North Korea continue to escalate. The isolated nation's missile tests have drawn the ire of President Donald Trump, while North Korean officials have indicated they are prepared for war.

The day before Pence arrives in South Korea, North Koreans will be celebrating the Day of the Sun, a holiday marking the anniversary of former President Kim il Sung's birth. North Korea has previously conducted weapons tests on holidays and anniversaries.

On Friday, North Korean Vice Minister Han Song Ryol told The Associated Press that it continues to improve nuclear weapons in "quality and quantity," suggesting that another test could be approaching.

Here's a look at North Korea's five previous nuclear tests:

Oct. 9, 2006

North Korea’s says they had their first underground nuclear test at Punggye-ri, also known as Punggye-yok, a remote area in the Northeast near the town of Kilju.

They say the blast was based on plutonium and its explosive force, relatively small, was less than 1 kiloton.

Pyongyang gave an advance warning to the international community, six days prior, of its intention to test the nuclear device.

Days later, the U.N. Security Council unanimously approved military and economic sanctions against North Korea.

May 25, 2009

Barely a month after North Korea walked out of international talks on its nuclear program, it claimed to conduct a second underground test, saying that they detonated a plutonium nuclear device.

This time, the power of the explosion was equivalent to U.S. bombs that destroyed Hiroshima and Nagasaki, Japan, in 1945.

Although North Korea did not specify the location, a 4.7-magnitude quake was detected near the first nuclear test site, Punggye-yok.

The claimed underground bomb test followed hard on the heels of the test of a long-range missile in April 2009.

North Korea claimed it succeeded, but the missile flew only 90 seconds after takeoff.

Feb. 12, 2013

North Korea claimed to launch its third underground nuclear test after unusual seismic activity was detected near the same Punggye-ri nuclear site.

The United States Geological Survey confirmed a magnitude-5.1 artificial earthquake.

This time North Korea claimed to have developed a lighter miniaturized nuclear device to fit on the top of the long-range missiles that could reach the mainland of United States.

South Korea’s Defense Ministry estimated the yield to be approximately 6 to 7 kilotons.

Jan. 6, 2016

The world was alerted to the possibility of another nuclear test when a 5.1 magnitude earthquake was measured at a location adjacent to the site of previous tests, a suspicion later confirmed by North Korean state television.

“We have perfectly succeeded in testing our first hydrogen bomb,” reported an anchor on the government-run station. “It was one hundred percent capable from our own wisdom, technology and power. We have now scientifically test-proved a miniaturized hydrogen bomb.”

State media later released photographs of Kim Jong Un signing what appeared to be an authorization for the test in December 2015.

Following the test, United Nations Secretary General Ban Ki-Moon said the action was "profoundly destabilizing for regional security" at an emergency meeting of the organization's Security Council.

A spokesman for the U.S. State Department added, "We condemn any violation of UN Security Council Resolutions and again call on North Korea to abide by its international obligations and commitments."

Sept. 9, 2016

In its largest nuclear test to date, North Korea conducted a warhead explosion that the U.S. Geological Survey registered at a 5.3 magnitude. The South Korean defense ministry estimated that the explosion was the equivalent of 10 kilotons of TNT.

Afterward, the White House told ABC News that President Barack Obama "indicated he would continue to consult our allies and partners in the days ahead to ensure provocative actions from North Korea are met with serious consequences."

In North Korea, the test was again touted as a success. On state television it was reported that the country "will continue to strengthen [its] nuclear capabilities to protect [its] sovereignty."

"We have now standardized and minimized nuclear warheads... We can now produce small nuclear warheads any time we desire." said a North Korean newscast.

Leaders from neighboring China, Japan and South Korea all spoke out in opposition to the test.