North Korea could be preparing its sixth nuclear weapon test, South Korea warned Monday.

The National Intelligence Service in Seoul told South Korean lawmakers that it’s seen signs that its northern counterpart is getting ready for another missile test at its Punggye-ri underground test site, according to CNN.

North Korea “has completed its preparation to carry out a nuclear test at Tunnel 2 and Tunnel 3 of the Punggye-ri nuclear test site,” Democratic Party lawmaker Kim Byung-kee said the NIS reported during a closed-door parliamentary meeting.

North Korea’s last nuclear test was last September when it claimed to have detonated a small nuclear warhead mounted on “strategic ballistic rockets” in its strongest test ever.

The country has been conducting such tests since 2006 — despite being banned by the UN and repeatedly sanctioned for doing so.