Deadly Israeli attacks that blew up Hezbollah radios and pagers crossed all red lines, the leader of the heavily armed Iran-backed Lebanese movement said on Thursday, as the United States called for restraint and urgent de-escalation.

Israel has responded to Hezbollah's attacks with strikes in southern Lebanon, and has struck senior figures from the group in the capital Beirut. The exchanges have killed hundreds in Lebanon and dozens in Israel and forced the evacuation of tens of thousands of residents on each side of the border.

The absence of a full-blown war in Lebanon has been touted as a core U.S. achievement, but now Washington’s grip on the crisis appears more tenuous than ever.