A homemade bomb ripped through a commuter bus in the southern Philippines on Thursday, wounding 27 people, police said.

The military initially reported three people were killed, but police and army officials later corrected themselves and said there were no deaths.

The bus had stopped at a Digos city terminal on the way to the regional center of Davao. Moments after the driver returned and started the engine, the blast shattered the windows and some of the seats, said provincial police chief Cesario Darantinao.

Police recovered broken nails used as shrapnel, he said.

The owner of the bus company, who is also the mayor of a nearby town, had complained of extortion demands purportedly coming from communist rebels, Darantinao said.

The company did not provide police with details of the threat, he said.

Among the 27 injured, four were in serious condition and brought to Davao Medical Center, one-hour drive from Digos, Darantinao said.

Apart from communist rebels, Muslim militants and extortion gangs also operate in the area.

The notorious extortion syndicate Al Khobar, which authorities say has ties to Muslim militants, has been terrorizing bus companies and has been blamed for planting several bus bombs in the region.

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Associated Press writer Teresa Cerojano contributed to this report.