In a show of force, the US flew a B-52 bomber low over South Korea on Sunday as a warning to the North Korean regime following the government’s fourth nuclear test, the Associated Press reported.

According to the US military, the B-52 was accompanied by South Korean 5-15 and US F-16 fighter jets. The planes returned to their base in Guam following the flyover.

“This was a demonstration of the ironclad US commitment to our allies in South Korea, in Japan, and to the defense of the American homeland,” explained Admiral Harry B. Harris Jr., commander US Pacific Command, in a statement. “North Korea’s nuclear test is a blatant violation of its international obligations.”

The last time the US conducted a B-52 flyover was in 2013, following North Korea’s third nuclear test.

On Wednesday, the North Korean government stated that it successfully carried out a nuclear test, detonating a Hydrogen bomb near the Punggye-ri nuclear testing site. The explosion set off a 5.1 magnitude earthquake in the northern part of the country.

In public comments made last week, North Korean dictator Kim Jong Un hailed the nuclear test as “a self-defensive step” that is meant to protect the country “from the danger of nuclear war caused by the US-led imperialists,” the Korean Central News Agency quoted him as saying.

During a tour of the People’s Armed Forces Ministry, Kim added, “It is the legitimate right of a sovereign state and a fair action that nobody can criticize.”

Since Wednesday, North and South Korea have been engaged in what can only be described as a “Cold War-era standoff.” On Friday, South Korea set up large speakers along the border and began blasting anti-Pyongyang propaganda, including news broadcasts and pop music, which can be heard up to 10 kilometers (6 miles) during the day and 24 kilometers (15 miles) at night.

In response, North Korea turned on its own border speakers to drown out the messages so its soldiers will not be influenced. In usual North Korean rhetoric, a top official warned that the South’s action are pushing the divided peninsula “toward the brink of war.”

According to South Korea’s Yonhap news agency, Seoul has deployed defensive weapon and missile systems near the border in preparation for a possible North Korean provocation.