Dubai, United Arab Emirates (CNN) -- Australia warned Israel Thursday of a possible diplomatic rift if Israel condoned the use of fraudulent Australian passports in the killing of a Hamas leader.

Israel's ambassador was given the warning after it was learned that three Australian passports were used by members of an alleged assassination crew connected to the recent slaying of a Hamas leader in a Dubai hotel room, Australia's Foreign Minister Stephen Smith said Thursday.

"I made it crystal clear to the ambassador that if the results of that investigation cause us to come to the conclusion that the abuse of Australian passports was in any way sponsored or condoned by Israeli officials, then Australia would not regard that as the act of a friend, "Smith said Thursday. " We would not regard that as the act of a friend."

The stern statement from Smith is part of the growing international diplomatic tiff stemming from the January 20 killing of Mahmoud al-Mabhouh, a founding member of Hamas' military wing.

Al-Mabhouh was found dead in his hotel room January 20. Police believe he was killed the night before and suspect the Mossad, the secretive Israeli foreign intelligence unit, was behind his slaying.

A total of 26 suspects have been identified by Dubai police. The suspects are believed to have acquired faulty passports to arrive in Dubai for the killing and then fled to other far-flung locations, police said.

The 26 named suspects do not include two Palestinians previously arrested in Jordan and returned to the UAE.

Twelve of the suspects used British passports, police said. Six suspects used Irish passports and four suspects used French passports. Along with the three suspects who used Australian passports, another suspect used a German passport .

The European Union this week condemned the use of false EU passports in connection with the al-Mabhouh slaying.

Authorities have not said how he died, al-Mabhouh's family was told there were signs of electric shocks on his legs, behind his ears, on his genitals and over his heart. Blood on a pillow led police to believe he was suffocated, the family was told. The killers left some of al-Mabhouh's medicine next to his bed in an apparent effort to suggest his death was not suspicious, police said.

Israeli Foreign Minister Avigdor Lieberman has said only "media reports" link Israel to al-Mabhouh's death.

CNN's Roya Shadravan contributed to this report.