Israeli warplanes carried out their most intense strikes on southern Lebanon in nearly a year of war, heightening the conflict between Israel and Lebanese armed group Hezbollah amid calls for restraint.

A senior U.S. official has confirmed to Fox News that Israel is behind the explosions of pagers used by members of Hezbollah in Lebanon.

Israel launched a series of strikes on Hezbollah targets Thursday as the war against the Lebanon-based group widened in the wake of two consecutive days of deadly explosions triggered in wireless devices.

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.

Israeli Defense Minister Yoav Gallant ushered in what he called a “new phase” in the war with regional Islamist groups and said troops would be diverted to the Lebanese border, an indication that long-held fears of a wider conflict may soon be realized.

Lebanese officials say more handheld devices exploded a day after thousands of pagers carried by Hezbollah members blew up in an attack blamed on Israel.