NAIROBI, Kenya — In the first killing of its kind, private security contractors shot dead a Somali pirate in a clash that left two skiffs riddled with bullet holes, officials said Wednesday.

The killing raises questions over who has jurisdiction over a growing army of armed guards on merchant ships flying flags from many nations.

There’s currently no regulation of private security onboard ships, no guidelines about who is responsible in case of an attack, and no industrywide standards, said piracy expert Roger Middleton from the British think tank Chatham House.