North Korea has reportedly rejected a visit by a United Nations delegation.

A U.S. diplomatic source said Sunday that a delegation led by U.N. Under Secretary-General for Political Affairs Lynn Pascoe had planned to visit North Korea early next month.

Pyongyang reportedly turned down the visit, saying it was an inappropriate time.

The canceled visit has hinted at U.N. Secretary-General Ban Ki-moon playing a role directly or indirectly in relieving growing tension on the Korean Peninsula.

Amid the North’s reported preparation to launch a missile, voices are urging the dispatch of a political heavyweight to Pyongyang as a special envoy. Former President Kim Dae-jung and former chairwoman of the ruling Grand National Party Park Geun-hye are possible candidates along with Ban.