MADRID (AFP) - Spain's government said on Thursday that a wave of small earthquakes that have rattled the country's eastern coast could be caused by a large offshore gas storage plant.

Over 300 earthquakes have struck the Gulf of Valencia, a zone not normally known for seismic activity, over the past month, according to Spain's National Geographic Institute. The quakes have not caused any damage but have frightened residents.

The strongest, a 4.2 magnitude earthquake, hit in the early hours of Tuesday.

Two earthquakes measuring 4.1 struck the region late on Wednesday.

Environmentalists blame the earthquakes on the injection of gas into a giant underground gas storage facility located in the Gulf of Valencia but the government has up to now said there was no confirmed link.

The Castor storage plant aims to store gas in a depleted oil reservoir 1.7 kilometres (1.05 miles) under the Mediterranean Sea and send it via a pipeline to Spain's national grid.

"There seems to be a correlation, a direct relationship between the gas injection in the underground storage facility which is 22 kilometres from the coast and the microearthquakes that have occurred," Industry Minister Jose Manuel Soria said in an interview with radio Cadena Cope.

Spanish firm Escal UGS which owns and operated the Castor storage plant stopped injecting gas into the underground reservoir on June 16.

Last week the industry ministry ordered that the injections be stopped while the possible link to the earthquakes was investigated and requested a detailed report from the country's National Geographic Institute on the seismic activity in the area.

The plant can hold up to 1.3 billion cubic metres of gas, enough to meet the needs for the region of Valencia which has a population of around five million people for three months.

About 100 million cubic metres has been injected into the plant so far.

"There are rational indications to think that the earthquakes are linked to the injection of gas in the Castor project," the president of Spain's College of Geologists, Luis Suarez, told AFP.

The plant is located near a fault line that normally produces very little seismic activity but the gas injections were causing the accumulated energy that exists there to be released, he said.