The US State Department said in a revised travel advisory 'terrorist groups' were continuing to plot possible attacks in Sri Lanka after 290 people were killed and about 500 wounded in blasts in churches and luxury hotels on Sunday.

"Terrorists may attack with little or no warning," it said in the revised warning, which was dated Sunday US time.

It said possible targets included tourist locations, transportation hubs, shopping malls, hotels, places of worship, airports and other public areas.