Protesters angered by an anti-Islam film made in the US have stormed the grounds of the American embassy in the Yemeni capital Sanaa.
Police shot in the air in an attempt to hold back the crowds, but failed to prevent them gaining access to the compound and setting fire to vehicles.
Security forces have now regained control of the compound.
On Tuesday, the US ambassador to Libya was killed in a fire started after the US consulate in Benghazi was stormed.
US officials say they are investigating whether the attack in Libya was planned, citing suspicions that a militant jihadist group may have co-ordinated the violence.
Three other US consul staff and several Libyans died in that attack, along with Ambassador J Christopher Stevens, who is believed to have died from smoke inhalation.
Security increased
Security force reinforcements in Sanaa used tear gas, water cannon and live fire to drive back protesters.
“We can see a fire inside the compound and security forces are firing in the air. The demonstrators are fleeing and then charging back,” one witness told the Reuters news agency.
The crowd has been pushed out of the compound, but protests are reported to be continuing outside. There were reports of injuries on both sides, although Reuters carried a statement from the embassy saying there were none.
It was not immediately clear whether the embassy was occupied at the time. There are reports that embassy staff have been moved to a safer location.
There have also been clashes over the past three days in the Egyptian capital, Cairo.
On Wednesday, demonstrators in Cairo angry at the film – Innocence of Muslims – breached the walls of the US embassy and tore down the flag. The clashes, which began on Tuesday, continued in the early hours of Thursday morning.
President Mohammed Mursi has appealed for calm, saying Egyptians “reject any kind of assault or insult” against the Prophet Muhammad.
“I condemn and oppose all who… insult our prophet. [But] it is our duty to protect our guests and visitors from abroad,” he said in a statement broadcast by state media.
I call on everyone to take that into consideration, to not violate Egyptian law… to not assault embassies.”
Security has been increased at US embassies and consulates around the world in response to the rising tensions.
A marine anti-terrorism team is being deployed to Libya to bolster security there, a US defence source told reporters in Washington, and the US is sending two destroyers to the Libyan coast as a precautionary measure.
US President Barack Obama has vowed to work with the Libyan authorities to bring those behind the Benghazi attack to justice.
Libyan officials have condemned the attack and pledged to investigate.
The White House says Mr Obama spoke by phone to Libyan President Mohamed Magarief on Wednesday evening and agreed the two countries should work together to identify the attackers.
Mr Obama has also spoken to President Mursi, the White House said.
Little is known about the origins of the film, including the man named as Sam Bacile whom is reported as being behind its production.