BEIRUT (Reuters) - Hezbollah leader Sayyed Hassan Nasrallah said on Friday that a future war waged by Israel against Syria or Lebanon could draw thousands of fighters from countries including Iran and Iraq.

People watch Lebanon's Hezbollah leader Sayyed Hassan Nasrallah as he appears on a screen during a live broadcast to speak to his supporters at an event marking Resistance and Liberation Day in Bekaa Valley, Lebanon, May 25, 2017. REUTERS/Hassan Abdallah

His comments indicated that the same array of Iranian-backed Shi’ite militias - but not countries - currently fighting in Syria in support of President Bashar al-Assad could take part in any future conflict with Israel.

Tensions have risen between Hezbollah and its longtime foe Israel in recent months since Donald Trump became U.S. president with his tough talk against Iran. Israel’s air force chief said his country would use all its strength from the start in any new war with Hezbollah.

“The Israeli enemy must know that if an Israeli war is launched against Syria or Lebanon, it is not known that the fighting will remain Lebanese-Israeli, or Syrian-Israeli,” Nasrallah said in a televised speech.

“This doesn’t mean there are states that might intervene directly. But this could open the way for thousands, even hundreds of thousands of fighters from all over the Arab and Islamic world to participate - from Iraq, Yemen, Iran, Afghanistan and Pakistan,” he said.

Nasrallah has repeatedly warned Israel against attacking Lebanon, where the Iran-backed Shi’ite group is based, and from where it sends fighters to support Assad against insurgents.

Experts on the group say the warnings are part of a policy of deterrence that has also included revealing some of its military capabilities.

Nasrallah said in recent months Hezbollah’s rocket arsenal can hit any military target in Israel, which is Lebanon’s southern neighbor.

He said any Israeli war with Lebanon or the Gaza Strip, which is run by the Palestinian Islamist movement Hamas, would be “very costly” and that Israel would not be able to win.

Israel has targeted senior Hezbollah commanders in air raids on Syrian soil. But there has been no major confrontation between Hezbollah and Israel in Lebanon since a month-long war between the two sides in 2006.