Reuters reported 2500 which i consider most accurate news source. But I did see other mentions of 5000 too
ca.finance.yahoo.com/news/latest-...
ca.finance.yahoo.com
The Latest: US deploying Marines to Middle East as it pounds Iran
About 2,500 U.S. Marines are being deployed to the Middle East as American and Israeli strikes keep pounding Iran and the Islamic Republic keeps attacking Persian Gulf shipping and energy infrastructu...