Somalia drought fuelling piracy – US Africa command head.
General Thomas Waldhauser, head of US Africa Command, said there had been half a dozen attacks in the last month.
About three million Somalis face food insecurity and a national disaster was declared last month.
Piracy was rampant off the Somali coast until increased patrols by European naval forces contained the problem.
US Defence Secretary Jim Mattis expressed concerns about the resurgence of Somali piracy during a visit to the American military base in Djibouti.
Mr Mattis suggested commercial vessels should consider stepping up onboard security to guard against attacks at sea, saying the situation is being monitored but there was no plan of an immediate response.
"We’re not ready to say there is a trend there yet but we’ll continue to watch."
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Exit player Last month, an oil tanker was hijacked by suspected pirates off the coast of Somalia, the first such hijacking in the region in five years.
The vessel was en route from Djibouti to the Somali capital, Mogadishu, and was then diverted towards the port of Alula in the semi-autonomous Somali region of Puntland.