STOCKHOLM — Swedish prosecutors are to investigate whether Israel broke international law when it boarded a number of aid ships that were attempting to defy an Israeli blockade of Gaza in 2010 and 2012.

The Swedish Prosecution Authority announced on Thursday “a preliminary investigation on the circumstances of the boarding by Israeli soldiers of ships heading to Gaza in May 2010 and October 2012.”

In the first case, Israeli troops attacked a six-ship aid flotilla in international waters, leading to the death of nine Turkish citizens on one of them, the Mavi Marmara.

In 2012, Israel’s navy seized another ship — again in international waters — the Estelle, a Finnish-flagged galley carrying humanitarian aid as part of the international Ship to Gaza campaign.

In both incidents, Swedish citizens were on board ships attempting to break the blockade.

Swedish legal authorities said the investigation will examine several reported cases of aggravated assault, aggravated theft and violation of international law, with regard to the Geneva Conventions, according to which civilians must be protected during armed conflicts.

The probe would not look into charges of hijacking and illegal detention which has been requested by the 22 Swedish plaintiffs.

Prosecutor Henrik Attorps, who formally opened the investigation, wrote that the alleged crimes fell under Swedish jurisdiction Sweden because they took place in international waters and affected Swedish citizens.

Swedish law allows for prosecutions related to violations of international law in other territories, however the prosecutors wrote that they would require Swedish government approval before any formal charges can be brought.

“No individual has been identified as a suspect for the crimes yet,” the prosecutors added.

The investigation was launched in response to complaints filed with police by the Swedish Ship to Gaza association as well as Swedes who were on board the ships and were taken into custody and later deported by Israeli authorities.