The U.S. and South Korea have agreed to the early activation of a defence system designed to shoot down North Korean missiles, according to South Korea's Yonhap news agency.

The decision to activate the Terminal High Altitude Area Defence (THAAD) system came during talks between the acting South Korean President Hwang Kyo Ahn and Mike Pence, as the U.S. Vice President warned North Korea that the "era of strategic patience is over", The Independent says.

At a joint press conference with Pence on Monday, April 17, Hwang said: "We have agreed to further strengthen the readiness posture of [the] ROK-U.S. alliance that matches the threats posed by North Korea through a swift deployment of THAAD."

A failed North Korean missile test on Sunday, when an unidentified projectile exploded moments after being launched in an eastern port city, came in defiance of U.S. President Donald Trump's demands for the country to wrap up its nuclear programme.

Operations to install the THAAD began in early March, the day after the North launched four ballistic missiles, when the United States flew in the "first elements" of the system to a military base near the South Korean capital Seoul.

It has a range of 200km, and is capable of destroying incoming warheads by intercepting them mid-flight. The system has previously been installed in Guam and Hawaii.

Speaking at the time, Chinese foreign spokesperson Geng Shuang said China was "firmly opposed" to the deployment, and would "resolutely take measures to defend our own security interests".