North Korea is deploying military aircraft to the east of the country after U.S. B-1B bomber jets arrived in South Korea over the weekend, NHK World reports.

The U.S. military has stepped up its air force cooperation with South Korea and Japan in the aftermath of a series of missile tests and a nuclear test by North Korea this summer. Speaking in South Korea Wednesday, U.S. Lieutenant General Thomas Bergeson said that a joint force with seamlessly integrated air power “is exactly that type of force that is necessary to interdict and then defeat a nuclear-capable enemy.”

According to South Korean intelligence, however, which national lawmakers were briefed about Tuesday, the North is shifting deployments to the east of the country, along the route that the U.S. jets flew. Interestingly the decision occurred after the U.S. made the announcement of the deployment public, suggesting the North may have been unaware of the jets beforehand.

A legislator at the meeting told South Korea’s Yonhap news agency that the North Korean military showed no immediate signs that it detected the planes’ arrival Saturday. This has led South Korean media to speculate about the state and management of the North’s early warning radar system as it nominally has a detection range of up to 600 kilometers (around 370 miles.)

The North Korean redeployment follows tense exchanges between the U.S. and North Korean delegations from the U.N. General Assembly floor this month, during which President Donald Trump called North Korea’s leader “rocket man” and warned him he is “on a suicide mission.”

North Korean Foreign Minister Ri Yong Ho responded to the comments this week, accusing Trump of effectively declaring war and said Pyongyang now had the right to shoot down U.S. military jets even if they do not cross into his country's airspace.