LONDON (AP) — Microsoft says it has detected hacking attacks aimed at European democratic institutions including think tanks and non-profit groups ahead of elections on the continent in May.

The company said Tuesday that a group called Strontium targeted email accounts for more than 100 people in six European countries working for the German Council on Foreign Relations, the Aspen Institutes in Europe and the German Marshall Fund.

Microsoft said in a blog post that it is continuing to investigate but is confident many of the attacks originated from Strontium, a group that others call Fancy Bear or APT28. U.S. authorities have tied the group to Russia's main intelligence agency, known as the GRU.

Microsoft said the attacks occurred from September to December, and that it notified the organizations after discovering they were targeted.