Two strong earthquakes on Sunday shook Iceland's largest volcano, which is on red alert for imminent risk of eruption, the Icelandic Met Office said.
A large explosion at the Bardarbunga volcano could signal a replay of the global travel chaos caused by the eruption of another Icelandic peak four years ago, which created a massive ash cloud across Europe.
The earthquakes were listed on the Met Office's website with intensities of 5.3 and 5.1 on the Richter scale, which makes them the strongest recorded in the region since the current seismic cycle began last week.
On Saturday, Iceland raised its alert over the Bardarbunga volcano to the highest level and closed airspace in the area, but all of Iceland's airports remained open.
Met Office official Gunnar Gudmundsson told Icelandic public broadcaster RUV that it was difficult to say whether the earthquakes indicated an increased risk of an eruption.
Earlier this week, authorities evacuated tourists and hikers from the area around the volcano, which is covered by a glacier. Seismologists had recorded an earthquake of 4.5 in the Richter scale on Monday, when Iceland decided to raise its aviation alert to orange, the second-highest level of five.
The eruption of Eyjafjoell, a smaller volcano, in April 2010 caused travel mayhem, stranding more than eight million people in the widest airspace shutdown since World War II.
Iceland's most active sub-glacial volcano Grimsvotn erupted in 2011, forcing the country to temporarily shut its airspace and sparking fears of a repeat of the Eyjafjoell flight chaos.
Iceland is home to more than 100 volcanic mountains, some of which are among the most active in the world.