Iceland's Meteorological Office has raised the aviation alert level around the Katla volcano because of seismic activity.
The activity, which began on Thursday and continued on Friday, prompted officials to raise the alert level to yellow, which signifies volcanic activity above background levels. There are two higher levels of alert.
Officials said they raised the alert due to "the unusually high level of unrest at the Katla volcano".
Katla is in southern Iceland, 140 kilometres (87 miles) from the capital, Reykjavik.
Civil Defence officials met on Friday and said they have begun contingency planning to prepare for any eruption.
Iceland is often hit by seismic activity.
In April 2010 ash from an eruption of the country's Eyjafjallajokull volcano grounded flights across Europe for days, stranding millions of people.