UPDATE 3-Shell resumes oil output at Nigeria EA field

* Traders estimate EA exports at 60,000-65,000 bpd in Aug

* Rebel group threatens further attacks despite ceasefire

* MEND says will release foreign hostages in 24 hours (Updates with MEND threat, possible hostage release)

By Randy Fabi

ABUJA, July 21 (Reuters) - Royal Dutch Shell (RDSa.L) said on Tuesday it has resumed oil output at its EA oilfield in Nigeria, a rare bright spot for an industry battered by a string of militant attacks in the last two months.

But hours after Shell's announcement, Nigeria's main militant group repeated its threat to revisit oil facilities that are repaired from previous attacks.

A Shell spokesman said offshore production resumed at its 115,000 barrel per day oilfield after being idle for three years because of security concerns.

"EA resumed production about three weeks ago and is slowly ramping up," said a Shell spokesman. He declined to say how much the field was currently producing.

Traders said EA oil shipments were estimated between 60,000 bpd and 65,000 bpd for August.