Is there a US embassy in Cuba?
Yes, there is. Here’s their contact info.
U.S. Embassy Havana
Address: Calzada between L & M
Vedado, Havana, Cuba
Tel: (53 7) 839-4100
The American Citizens Services Unit at the US Embassy in Havana is open to walk-in customers seeking emergency consular services from 8:00 am until 4:30 pm Monday through Thursday, and from 8:00 am until 3:30 pm on Friday, except on Cuban and U.S. federal holidays.
For emergencies involving American citizens outside normal business hours, please call +53 7 839 4100 and dial 1 to select English and then 0 to speak to an operator.
American citizens should show their American passports to Embassy security when they approach the Embassy.