Mohammed Al-Qubati, the director of a field hospital at the main protest site in Sanaa dubbed “Change Square,” said that dozens more were injured in the Tuesday protests demanding the overthrow of President Ali Abdullah Saleh.

Tens of thousands of protesters marched through Sanaa led by shirtless young men with the words “Leave ... you butcher,” referring to Saleh, scrawled across their chests.

Pre-dawn fighting between troops loyal to Yemen’s embattled leader and rival forces killed at least 18 people in Sanaa on Monday, reviving fears of civil war in the Arabian peninsula nation.