A U.N. envoy is warning that Hezbollah's involvement in the conflicts in Syria and Iraq risks a spillover of sectarian tensions into Lebanon, where the Islamic State extremist group and the al-Qaida-linked Nusra Front are reported to be expanding.

Terje Roed-Larsen expressed serious concern Friday that not only have Hezbollah and other militias continued their activities since the Security Council ordered them to disband in 2004 "but if anything they have expanded." He also expressed concern at the reported expansion of extremist groups, mostly in Palestinian refugee camps.

He called for the urgent disbanding of all militias in his final briefing to the council before relinquishing the post on May 31, saying "their growing capabilities ... represent a major and dangerous threat to Lebanon's sovereignty, stability and political independence."