North Korea ordered the assassination last year of its leader’s estranged half brother with a banned nerve agent, an act that has caused the United States to impose new sanctions on the country, the State Department said on Tuesday.

The announcement by the State Department came on the same day that South Korean officials said the North was willing to talk with the United States about ending the crisis over its missiles and nuclear arsenal.

Kim Jong-nam, the half brother of Kim Jong-un, North Korea’s leader, was killed Feb. 13, 2017, with VX, a deadly nerve agent used in prohibited chemical weapons of mass destruction that North Korea is known to have stockpiled.

Kim Jong-nam, who had criticized the dynastic succession in North Korea but had professed no interest in politics, was ambushed at the Kuala Lumpur International Airport in Malaysia by two women who smeared his face with VX. The women were arrested.