Syrian activists say Islamic State (IS) fighters have briefly overrun a hospital in the eastern city of Deir al-Zour.
The attack, which started at dawn on May 14, was centered on Assad Hospital, to the west of the besieged city.
The British-based Syrian Observatory for Human Rights said some 35 pro-government fighters were killed and some medical staff taken hostage. At least 24 IS fighters also died.
Government forces retook the hospital after several hours of fierce fighting, but the fate of the hostages is unclear.
Local Coordination Committees, an opposition network in Syria, said IS fighters also captured university dorms and grain silos in their advance.
Deir al-Zour is in an oil-rich area and on a vital supply route to the IS stronghold of Raqqa.
Meanwhile, a suicide attack claimed by IS has killed at least 25 people in the southern Yemeni city of Mukalla.
Many of the victims appear to be recruits who were lining up at a police headquarters.
In a message on its online news agency Amaq, IS said the attacker was a "martrydom-seeker" who had detonated his explosive belt.
The city was long a hub for Al-Qaeda militants before the group was pushed out last month in a military offensive by government troops backed by the United Arab Emirates.
Their militant rivals in Yemen's branch of IS have launched a series of suicide attacks on all sides in Yemen's ongoing civil war.
The U.S. military announced last week it had deployed a small number of personnel to Yemen to aid in the fight against Al-Qaeda in the Arabian Peninsula (AQAP).