U.S. missile launchers and other equipment needed to set up a controversial missile defense system have arrived in South Korea, the U.S. and South Korean militaries said Tuesday, a day after North Korea test-launched four ballistic missiles into the ocean near Japan.

The plans to deploy the Terminal High-Altitude Area Defense system, or THAAD, by the end of this year have angered not only North Korea, but also China and Russia, which see the system’s powerful radars as a security threat.

Washington and Seoul say the system is defensive and not meant to be a threat to Beijing or Moscow.

The U.S. military said in a statement that THAAD is meant to intercept and destroy short and medium range ballistic missiles during the last part of their flights.

“Continued provocative actions by North Korea, to include yesterday’s launch of multiple missiles, only confirm the prudence of our alliance decision last year to deploy THAAD to South Korea,” Adm. Harry Harris, head of the U.S. Pacific Command, said in the statement.

Some South Korean liberal presidential candidates have said that the security benefits of having THAAD would be curtailed by worsened relations with neighbors China and Russia.