(Corrects to make clear in penultimate paragraph that the merchant ship boarded earlier this year was not hijacked)

MOGADISHU, Oct 30 (Reuters) - Somali pirates have freed seven Indian sailors detained for close to four years in exchange for an undisclosed ransom, Somali officials and a maritime monitoring group said on Friday.

At one time the pirates made millions of dollars in ransoms from seizing ships sailing the Horn of Africa nation's waters, but increased patrols by international navies on the Indian Ocean have reduced incidences of piracy.