A consortium consisting of retired American admirals, generals, ambassadors and senior government executives expressed deep concern Friday over the current escalation with Iran.
"A war with Iran, either by choice or miscalculation, would produce dramatic repercussions in an already destabilized Middle East," said the group in a letter addressed to U.S. President Donald Trump.
Signed by 76 people, the letter was published Friday by the War on the Rocks website.
It came hours before Trump's announcement that 1,500 additional U.S. troops will be sent to the Middle East amid heightened tensions between Tehran and Washington.
A war would "drag the United States into another armed conflict at immense financial, human and geopolitical cost", the letter warned.
It said lack of direct communication between the two countries' political and military leaders only increases the possibility of a miscalculation resulting in unintended military conflict.
The signatories urged Trump to immediately reduce the dangerous levels of regional tension.
"Crisis de-escalation measures should be established with the Iranian leadership at the senior levels of government as a prelude to exploratory diplomacy on matters of mutual concern," they wrote.
Earlier this month, the U.S. sent a carrier strike group and bomber task force to the Middle East, citing a "credible threat" from Tehran.
The Trump administration has also designated the Islamic Revolutionary Guard Corps, a branch of Iran's armed forces, as a terrorist group. In response, Iran designated U.S. Central Command as a terrorist group, creating the potential for a clash between the two sides in the Middle East.
By Servet Gunerigok in Washington