As the Constitutional Court approved the president's impeachment, the allies are expected to advance the deployment before a presidential election takes place in South Korea in early May.

"The THAAD deployment is the allies' decision. It will be pushed forward regardless of future political schedules," a military official told reporters.

In July last year, Seoul and Washington agreed to deploy a THAAD battery in South Korea to better counter growing nuclear and missile threats posed by North Korea.

Seoul and Washington have said the system is purely defensive and poses no threat to other countries in the region. But China has opposed it, arguing the system's powerful radars could spy on its flights and missile launches.

The liberal Democratic Party and other minor parties have demanded the issue of deploying a THAAD battery be reconsidered under a new government.

The US and South Korean militaries began to deploy the THAAD system on Monday night. 

Two missile launchers and other equipment of the system arrived at Osan Air Base in Pyeongtaek, 70 kilometers south of Seoul.

The radar system for THAAD will be delivered within this month to undergo an operational test and to be installed as early as possible, military officials said.

A THAAD battery consists of six truck-mounted launchers, 48 interceptors (eight per launcher), a fire control and communications unit, and an AN/TPY-2 radar.

THAAD is designed to intercept short and mid-range missiles, such as Scud and Rodong, which have a range of up to 3,000 km at altitudes of 40-150 km.

In a historic ruling Friday, the Constitutional Court formally removed impeached President Park from office over a massive corruption scandal that has plunged the country into political chaos. (Yonhap)