Two people were found dead at a two-alarm fire at a vacant apartment building in Southeast Washington.

District of Columbia firefighters got a call about 10 a.m. Tuesday for a fire at 1704 R St. SE in the Anacostia neighborhood and found the boarded-up two-story apartment fully engulfed in flames.

Dozens of firefighters attacked the fire but were ordered out of the building when the fire became too intense, said D.C. fire department spokesman Lon Walls.

After the fire was brought under control about 11 a.m., firefighters re-entered the building and found the two bodies near the front entrance, Walls said.

Later Tuesday, D.C. police and fire marshals were still investigating the cause of the fire and the deaths and what the two people were doing inside the vacant four-unit property.

Preliminarily, investigators are saying the fire was accidental, Walls said.

Three firefighters suffered minor injuries and were treated at area medical centers. One firefighter suffered a broken ankle, and two others suffered shoulder injuries.

The bodies have not been identified. They are the first two fire fatalities of 2013 in the District. Last year, there were eight fire deaths in the city after six of them in 2011.

Barbara Clark, the advisory neighborhood commissioner who represents the area where the fire occurred, said the building had been boarded up for a while.

"When buildings are boarded up, people break into them. Nobody complains about what they do, so they do what they want," Clark said. "It's tragic whenever anybody dies."

Authorities said the victims could have been squatters or drug users.