United Nations Special Envoy to Yemen Martin Griffiths is seen during a news conference at Johannesberg Palace, north of Stockholm, Sweden December 10, 2018. TT News Agency/Stina Stjernkvist via REUTERS/File Photo

CAIRO (Reuters) - U.N. Yemen envoy Martin Griffiths expressed alarm on Thursday over an escalation of violence there and urged all parties to exercise restraint.

Earlier in the day, the Iranian-aligned Houthi group used drones to attack a Yemeni government military parade in Lahaj province, killing several people, Saudi and Houthi media reported.