The aviation industry has been warned about the possibility of flight disruptions caused by activity at Iceland's largest volcano system.
Intense seismic tremors have been recorded at Iceland's Bardarbunga volcano for the past three days, although there are no signs yet of an eruption.
The country's Met Office has raised the risk level to the aviation industry to orange - the fourth level on a five-level scale.
The Met Office said in a statement that the strongest earthquake in the region since 1996 was recorded early on Monday.
"As evidence of magma movement shallower than 10km (6.2 miles) implies increased potential of a volcanic eruption, the Bardarbunga aviation colour code has been changed to orange," the statement said.
"Presently there are no signs of eruption, but it cannot be excluded that the current activity will result in an explosive sub-glacial eruption, leading to an outburst flood and ash emission."
In 2010 an ash cloud caused by the eruption of Iceland's Eyjafjallajokull volcano shut down much of Europe's airspace for six days.
More than 10 million people were affected by the disruption.
Bardarbunga is Iceland's largest volcanic system. It is located under the ice cap of the Vatnajokull glacier, in the country's south-west.
Met Office seismologist Martin Hensch said the risk of any disruptive ash cloud similar to the one in 2010 would depend upon several factors, including how high any ash coming from the volcano would be thrown.
He added that the biggest risk in Iceland would be caused by flood waves from an eruption beneath the glacier.
Original headline: Airlines Warned Over Iceland Volcano Eruption
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