Helsinki  - Explosives experts have defused a World War I hand grenade stored for years at a museum in the Aland Islands, located in the Baltic Sea between Finland and Sweden.

Some 30 years ago, a woman found the Russian-made grenade when digging in her garden in Mariehamn, the only town on the islands, news agency STT reported.

She put the grenade, the size of an orange, in her car and drove off to the Aland Islands museum where museum staff since have kept it on various shelves believing it did not pose a danger.

In December, museum staff decided to check if the grenade was armed or not and contacted explosives experts.

Using an X-ray machine they determined that the grenade was live, and disarmed the grenade on Thursday. The casing has been returned to the museum, STT said.

The grenade was believed to originate from a Russian munitions depot in Mariehamn.

The autonomous islands were once part of Sweden, but were ceded to Russia in 1809 together with Finland. The Aland islands have remained part of Finland since Finnish independence in 1917.

The Aland Islands have been demilitarised since 1921. (dpa)