The group in a statement questioned the international community's "shameful silence" in the face of "the tyranny of the Zionist entity," urging Islamic nations and "free peoples" to take immediate action to counter the aggression.
The Union urged Islamic and international governments to take decisive and immediate action to prevent humanitarian disasters that endanger international peace and security.
Earlier Saturday, the Iranian armed forces announced an increase in the death toll from two to four soldiers in an overnight Israeli airstrike, adding that Israeli fighter jets used US-controlled airspace over Iraq to launch long-range missiles at Iranian military sites.
This direct strike on Iranian military sites follows recent Iranian missile attacks against Tel Aviv in retaliation for the deaths of Hezbollah leader Hassan Nasrallah, Hamas leader Ismail Haniyeh and Islamic Revolutionary Guard Corps commander Abbas Nilforoushan.
Iranian military officials had previously warned that any attack from Israel would be met with a “harsher response.”

Israel flagrantly violates borders, UN norms
IUMS also expressed concern about Israel's escalating brutal attacks on the Gaza Strip and Lebanon, citing flagrant border violations as well as airstrikes on Iran.
It said Israel is violating international laws and UN norms, citing attacks on civilian infrastructure such as hospitals, residential buildings, mosques and schools sheltering displaced Palestinians.
The statement emphasized the need for immediate international intervention to prevent further escalation, warning that continued inaction would lead to more regional instability.
Flouting a UN Security Council resolution demanding an immediate cease-fire, Israel has continued a devastating offensive on Gaza since an attack last year by the Palestinian resistance group, Hamas.
Nearly 43,000 people have since been killed, mostly women and children, and over 100,000 injured, according to local health authorities.
Israel also faces a genocide case at the International Court of Justice for its actions in Gaza.