One of the largest aftershocks since the tsunami quake six days ago was registered in the sea off the Indonesian city of Banda Aceh, the US Geological Survey said, but was not expected to cause damage.
Survey spokeswoman Ms Kathleen Gohn said there were no initial reports that the 6.5 magnitude earthquake, 215 miles from Banda Aceh, had been felt in Indonesia.
It was one of the strongest of dozens of aftershocks since Sunday's 9.0-magnitude quake - one of the largest on record - triggered a devastating tsunami across the Indian Ocean.
The latest aftershock struck at about 6.25 a.m. Irish time (1:25 p.m. in Indonesia) at a depth of six miles.
"It was far enough away from Banda Aceh that I would not expect there to be any damage," Ms Gohn said.
On the same day as the tsunami, aftershocks with magnitudes of 7.1 and 6.6 were centred on India's remote Nicobar Islands in the Indian Ocean. Today's was the strongest since then.
Aftershocks in the region have become a daily event since Sunday and have rattled homes and shelters in the city for several nights running, sending many people scurrying outside.
Banda Aceh and the surrounding area, on the northern tip of the island of Sumatra, bore the brunt of the devastation from the tsunami, with some 80,000 people killed in the area.