TEHRAN - The death toll in a string of earthquakes that have rocked Indonesia's Lombok island over the past two months has reached 555 with nearly 1,500 injured, the disaster agency said Friday, adding that hundreds of thousands have been rendered homeless.

The picturesque island next to holiday hotspot Bali was hit by two deadly quakes on Jul 29 and Aug 5. On Sunday it was shaken by a string of fresh tremors and aftershocks, with the strongest measuring 6.9 magnitude.

Many victims were killed by falling debris as the tremors rippled across the island, causing widespread devastation, according to a report in Channel News Asia. Whole communities were flattened, leaving cracked streets lined with rubble, caved-in roofs and collapsed buildings.

About 390,000 people remain displaced after the quakes, the disaster agency said. "We've deployed troops to isolated villages that are difficult to reach," disaster agency spokesman Sutopo Purwo Nugroho said in a statement.

Aid organizations have vowed to step up humanitarian assistance on the island as devastated residents struggle in makeshift displacement camps. They warned that access to food, shelter and clean water has been insufficient for some residents displaced by the disasters.

Indonesia sits on the so-called Pacific "Ring of Fire", where tectonic plates collide and many of the world's volcanic eruptions and earthquakes occur. In the past, the country has been hit by many devastating quakes, including the one in 2004 when a massive 9.1 magnitude quake struck off the coast of Sumatra and killed 220,000 throughout the region.