Iran-aligned Iraqi armed group Kataib Hezbollah warned on Sunday it would resume attacks on U.S. troops in the region if the United States intervenes in the conflict between Israel and Iran.

The conflict, the most intense fighting between the two countries in decades, has been met in the United States with feelings of “frustration and helplessness,” as well as heartbreak.

The deadly conflict between Israel and Iran has entered a fourth day, with both sides firing waves of missiles overnight. Follow for live updates.

Israel and Iran have opened a new chapter in their long history of conflict. Israel launched a major attack with strikes early Friday that set off explosions in the Iranian capital of Tehran.

The Lebanese militant group Hezbollah was long considered Iran’s first line of defense in case of a war with Israel

Israel unleashed airstrikes across Iran for a third day and threatened even greater force as some Iranian missiles evaded Israeli air defenses to strike buildings in the heart of the country