Five crew members of an oil tanker seized by pirates off the coast of Somalia were killed before local security forces retook the vessel, a senior regional official has told the BBC.Puntland Deputy Information Minister Bile Qabowsade said the five were killed by pirates before regional forces boarded MT Hoarner 25.He said the dead included three Pakistani nationals, one Indian and one national of Myanmar. Four other crew members were injured, including three Pakistanis and one Indian.The tanker, which was carrying about 18,500 barrels of oil destined for the Somali capital, Mogadishu, was seized in April by six armed men while sailing off the coast of Somalia.Sixteen suspected pirates have been arrested, while others escaped and were being pursued, officials said.Qabowsade rejected suggestions that forces from Puntland, a semi-autonomous region of Somalia, had helped some of the pirates escape. The authorities have not given further details how the five crew members were killed or how the pirates took control of the vessel.The hijacked tanker was anchored near the Somali coast between the fishing towns of Xaafun and Bander Beyla.In April, officials had said there were 17 crew members on board when the vessel was hijacked. They included 10 Pakistanis, four Indonesians, one Indian, one Sri Lankan and a Myanmar national.Piracy off the Somali coast fell sharply after 2011 following international naval operations, but attacks and hijackings have increased again in recent years.