Debris lays strewn at the site of a bomb attack inside a Shi'ite mosque in Baghdad May 27, 2014. REUTERS/Thaier Al-Sudani

BAGHDAD (Reuters) - A suicide bomber blew himself up inside a Shi’ite mosque in central Baghdad on Tuesday, killing at least 19 people, security and medical sources said.

A Reuters photographer at the site of the blast in the busy district of Shorja said the mosque’s walls were blackened with smoke, blood streaked the ceiling, and prayer mats were strewn around.

Most of the victims were merchants and shopkeepers from the area who had gone to pray. Policeman Abbas Inad told Reuters: “The bomb was so big and stuffed with tiny metal balls to kill as many people as possible.”

It was not immediately clear who was behind the bombing, but Sunni Islamist insurgents have been regaining momentum in Iraq and have previously claimed responsibility for attacking Shi’ite places of worship.

Security and medical sources earlier said the bomb had exploded at an open-air bus station within range of the mosque.

The injured were rushed to nearby hospitals but the rescue effort was hampered by blast walls surrounding the market designed to limit the damage of an explosion.

Hospital sources said the death toll was likely to rise due to the severity of the injuries.