Lebanon's Hezbollah chief Sayyed Hassan Nasrallah said on Tuesday any aggression against Jerusalem or its holy sites would mean regional war.
Nasrallah's comments, in a televised speech, were his first since a cease-fire ended the fiercest fighting in years between Israel and Gaza-based Islamist militant group Hamas.
The Israel-Hamas hostilities were set off on May 10 in part by Israeli police raids on the Al-Aqsa mosque compound in Jerusalem's Old City and clashes with Palestinians during the Muslim holy month of Ramadan.
"When holy sites face serious threats there are no red lines," Nasrallah said. "All the resistance movements can't sit back and watch if holy sites are in danger."
The Iranian-backed Lebanese group is a staunch opponent of Israel and Nasrallah's speech marked the commemoration of Israel's withdrawal from southern Lebanon in 2000.
- Just as Hezbollah is Iran's strategic asset in Lebanon, Israel has Hamas in Gaza
- With tensions still simmering post cease-fire, Netanyahu faces three new challenges
- A new U.S. approach to Hamas could be in the making
Nasrallah also said that the fighting showed Hamas had greatly advanced its rocket capabilities, which he said was a big military achievement.
"They had the ability to launch rockets for 11 days and they could continue," he said.