The US and South Korea agreed Thursday to take “swift punitive measures” against North Korea if provoked — while a Pyongyang official vowed the North would conduct nuclear and missile tests to counter Uncle Sam’s “hostile acts.”

The war of words erupted as a North Korean propaganda outlet released a video showing a mock attack on the White House, declaring “the enemy to be destroyed is in our sights,” the Washington Post reported.

Images of the White House and aircraft carriers marked by cross hairs are shown in the 2½-minute video, released by the Meari, or Echo, website of North Korea.

“When the enemy takes the first step towards provocation and invasion,” reads a caption along with footage of the carrier exploding in a ball of flames and scenes from an April 15 military parade that marked the anniversary of the birth of the state’s founder, Kim Il Sung.

Against a background of missile launches, the caption reads: “We will show you what a strong country that leads the world in nuclear and missile technology is capable of.”

The video emerged a day after US troops delivered the components of the Terminal High Altitude Area Defense (THAAD) missile-defense system to South Korea.

The US said Thursday that it plans to activate the system in a matter of days, not late this year, and tighten economic sanctions against Pyongyang.

Adm. Harry Harris, head of the US Pacific Command, said THAAD would be “operational in the coming days to be able to better defend South Korea against the growing North Korea threat.”

He said the system is designed to bring strongman Kim Jong Un “to his senses, not to his knees,” the BBC reported.

The nuclear submarine USS Michigan, which carries Tomahawk cruise missiles, has already docked in the South Korean port of Busan. And the USS Carl Vinson carrier group will be arriving in the Korean peninsula area this weekend.

After a special briefing for all 100 US senators, top US officials announced President Trump’s strategy on North Korea.

“The president’s approach aims to pressure North Korea into dismantling its nuclear, ballistic missile, and proliferation programs by tightening economic sanctions and pursuing diplomatic measures with our allies and regional partners,” said a joint statement issued by Secretary of State Rex Tillerson, Defense Secretary Jim Mattis and Director of National Intelligence Dan Coats.

A White House official said the administration was considering putting North Korea back on the State Department’s list of countries that sponsor terrorism, the BBC reported.

Meanwhile, China on Thursday welcomed an apparently softer tone by the US on the North Korean nuclear and missile crisis but stressed its opposition to the THAAD system.

“The deployment of the THAAD anti-missile system in South Korea damages the regional strategic balance and stability. The Chinese side is resolutely opposed to this,” Defense Ministry spokesman Yang Yujun told reporters, according to Reuters.

“China’s military will continue to carry out live-fire military exercises and test new military equipment in order to firmly safeguard national security and regional peace and stability.”