The Islamic militant Hamas group ruling the Gaza Strip says it has executed three Palestinians accused of 'collaborating' with Israel.

Hamas says they were hanged at a police compound on Thursday morning as dozens of Hamas leaders and officials watched.

Hamas has launched a local media campaign against those it suspects of spying for Israel after a militant, Mazen Faqha, was found dead in Gaza last month.

Israel had sentenced him to nine life sentences for directing suicide bombings. He was freed along with more than 1,000 other Palestinian prisoners in exchange for a single Israeli soldier in 2011.

Hamas has executed 25 people sentenced under its judicial system since 2007 when it took over Gaza. Hamas also killed 23 people without trials during its 2014 war with Israel.