A Lebanese judge leading the probe into Beirut's deadly port blast issued new arrest warrants on Monday for two officials and three Syrian workers, a judicial source said.
"Investigating judge Fadi Sawan interrogated director of land and maritime transport, Abdel Hafiz Kaissi, and director of the port, Mohammed al-Mawla... then issued arrest warrants against them," the source said.
He then questioned and issued arrest warrants for three detained Syrian workers who had allegedly carried out welding at the port's warehouse number 12, hours before the explosion, the source added.
The move brings to 21 the number of people arrested in Lebanon's probe into the monster blast at Beirut's port on August 4 that killed at least 188 people, wounded thousands and ravaged swathes of the city.
Hundreds of tonnes of ammonium nitrate had been stored unsafely in the warehouse for at least six years, it emerged after the explosion, sparking widespread outrage over alleged official negligence that many said was to blame for the blast.
Sawan was expected to question four more port officials on Tuesday, the source said.
It remains unclear what exactly sparked the explosion.
Security sources have suggested welding work could have started a fire that triggered the blast, but some observers have rejected this as a theory pushed by the authorities.
Lebanon has refused an international investigation into the country's worst peace-time disaster, but the Lebanese probe is being aided by foreign experts, including from the US Federal Bureau of Investigation.
France, which counted among the dead several of its citizens, has launched its own enquiry.