The Icelandic Met Office say one of the tremors measured 3.7
Iceland has raised its warning level to aircraft after two earthquakes hit one of the country's biggest volcanoes.
The Icelandic Met Office said the quakes, one of which had a magnitude of 3.7, shook the Katla Volcano in the south of the country.
They are the strongest tremors since quakes raised concerns over a possible eruption of Katla last month.
Meteorologists said an "intense seismic swarm" had been recorded since Thursday morning.
Earthquake swarms occur when sequences of quakes strike in a relatively short period of time.
The Icelandic Met Office said: "Due to the unusually high level of unrest at the Katla volcano, we raise the aviation colour code from green to yellow."
Yellow is the second lowest of the four-colour warning scale.
The Katla Volcano has not had a major eruption since the beginning of the last century, but scientists think a large eruption is overdue.
However, they admit it still might be decades before it happens.
Last month, the volcano was rocked by two quakes measuring 4.5 and 4.6 in magnitude, a level not recorded since 2011.
In April 2010, the nearby Eyjafjallajokull Volcano erupted, causing a major part of Europe's airspace to be closed for several days.