Dubai, United Arab Emirates (CNN) -- Police announced 15 new suspects in the January killing of a Hamas leader at a Dubai hotel, bringing to 26 the number of people suspected of involvement in his death.



Authorities previously had released a list of 11 suspects in the 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 killing.



Among the new suspects are six more people who allegedly used British passports in the commission of the crime, four others using Irish passports, two other French passport holders and three people, including a woman, traveling on Australian passports, police said in a statement Wednesday.



The total number of suspects using British passports is now at 12, police said, along with six Irish passport holders and four French passport holders. Another suspect using a German passport was announced earlier this month. The three Australian passports are new.



"Friendly nations who have been assisting in this investigation have indicated to the police in Dubai that the passports were issued in an illegal and fraudulent manner, adding that the pictures on the travel documents did not correspond to the original owners," the police statement said.



Dubai authorities have informed Australia of the possible use of the three Australian passports, Australian Foreign Minister Stephen Smith said Thursday (Wednesday ET) in a statement to Parliament.



The passports were issued in 2003 to Joshua Bruce, Adam Korman and Nicole McCabe, he said, adding that Australian officials have been cooperating with Dubai authorities.



"The Australian government is very gravely concerned that these Australian passports appear to have been used fraudulently," he said.



Preliminary analysis shows that the passports "appear to have been duplicated or altered," he said.



"At this stage, Australian officials have no information, no information to suggest that the three Australian passport holders were involved in any way, other than as victims of passport or identity fraud."



He said he had told the Israeli ambassador to Australia, Yuval Rotem, that Australia expected Israeli authorities "to cooperate fully and transparently with the Australian Federal Police investigation into this matter."



The European Union earlier this week said it "strongly condemns" the use of false EU passports in connection with al-Mabhouh's slaying. Officials have said the passports are not fake or forged but were authentic passports meant for other people.



While 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.



Police said Wednesday they have traced the suspects' travel routes and their destinations before and after al-Mabhouh's death. "The suspects gathered in Dubai and dispersed to various locations before pairing up again in different teams and heading off to other destinations," the statement said. The Australians, for instance, are believed to have departed Dubai in a boat for Iran.



Police released a diagram showing the travel routes. The suspects are believed to have departed Dubai for places including Paris, Hong Kong and Rome following al-Mabhouh's death.



In addition, police said in a statement that 14 of the suspects used credit cards issued by MetaBank, based in the U.S. state of Iowa, to book hotel rooms and pay for air travel.



Payoneer, an online payment distribution service, issues the types of cards the suspects are said to have used through MetaBank. Someone "loads" the cards by paying Payoneer, which then contacts MetaBank to issue the card, according to Payoneer.



"We are aware of the news reports," Mary Kae Marinac, a spokeswoman for Payoneer, said Wednesday. "We are cooperating with [MetaBank] and
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