UPDATE 3-Nigerian rebel leader welcomes amnesty offer

* Government says to free militant leader after deal reached

* Terms of amnesty and release still under discussion

* Main militant group still unhappy with amnesty programme

(Adds MEND comment, paragraph 9, 18)

By Randy Fabi

ABUJA, July 9 (Reuters) - Nigerian militant leader Henry Okah, who is on trial for gun-running and treason, welcomed a government amnesty offer and could soon be released, lawyers told Reuters on Thursday.

Okah is the suspected leader of the Movement for the Emancipation of the Niger Delta (MEND), the region's main militant group, whose attacks in the last six weeks have wreaked havoc on Nigeria's oil sector.

If Okah is released, it would raise hopes that other militants would lay down their weapons in the Delta, the heart of Africa's biggest oil and gas industry.