Authorities in Dubai say they have identified several "European passport holders" as suspects in the killing of a Hamas military commander last week, BBC reported.
Preliminary investigations indicated Mahmoud al-Mabhouh was murdered by "a professional criminal gang" which followed him there, police said.
The suspects are thought to have fled the United Arab Emirates.
Hamas claims Israel killed Mr Mabhouh, a founder of the Izzedine al-Qassam Brigades. Israel has not commented.
Earlier, thousands of people attended the funeral of the 50-year-old in the Syrian capital, Damascus, where he had lived since 1989.
The exiled Hamas political leader, Khaled Meshaal, said: "I say to you Zionists, do not rejoice. You killed him, but his sons will fight you."
"God already took our leaders and loved ones, but resistance goes on. Palestine is a blessed land. It will not remain patient."
'Electric shock'
Earlier one member of the Hamas political bureau in Damascus, Izzat al-Rishq, told the BBC that Mr Mabhouh had been killed in his hotel room in Dubai on 20 January, a day after arriving on a visit, and that an investigation was under way.
He did not give any details about how Mr Mabhouh died, but his family said doctors who had examined his body determined that he had died after receiving a massive electric shock to the head. They also found evidence that he had been strangled, they added.
Blood samples sent to a French laboratory confirmed he was killed by electric shock, after which the body was sent to Syria, they said.
Mr Mabhouh's family also said he had survived two Israeli assassination attempts, including a poisoning six months ago in the Lebanese capital, Beirut, which left him unconscious for 30 hours.
Later, Dubai's government said police had identified suspects in the murder, describing them as "mostly holders of European passports", and saying that they were working with Interpol to apprehend them.
"Preliminary investigations indicate that the crime was committed by a professional criminal gang that was following the victim before he came to the United Arab Emirates" on 19 January, a statement said.
Hundreds of people took to the streets as Mr Mabhouh's coffin was paraded
"The culprits left a trace behind which points to them and will help in chasing and arresting them," it added.
Dubai police chief Dhahi Khalfan Tamim also fuelled speculation of Israeli involvement.
"I cannot rule out the possibility of Mossad [Israeli secret service] involvement in the assassination of Mabhouh," he told al-Jazeera television.
He said he could not announce the nationalities of the suspects.
Hamas said earlier that it had delayed the announcement of Mr Mabhouh's death in an attempt to "reach the Israeli agents who implemented this operation".
An Israeli government spokesman would not comment when contacted by the BBC, in line with Israel's usual policy on similar allegations.
Interpol hunt
Hamas officials told the BBC that Mr Mabhouh, a founder of the Izzedine al-Qassam Brigades, had been very close to Mr Meshaal.
Before moving to Damascus, he had been responsible for a number of attacks on Israeli targets and the abduction in 1989 of two Israeli soldiers, Sgt Avi Sasportas and Sgt Ilan Saadon, who were both later killed, they added.
He spent several periods in Israeli custody. After his last release, "he spent his life being hounded by the Zionist occupier until he succeeded in leaving the Gaza Strip," Hamas said in a statement.
"Our brother had been a target for the occupier ever since his participation in the kidnapping operation against the two Zionist soldiers, and for his role and support for the resistance."
The Izzedine al-Qassam Brigades, Hamas's military wing, has carried out hundreds of attacks and suicide bombings targeting Israelis.
These include launching rockets from the Gaza Strip into Israeli territory, the main reason the Israeli military gave for launching a 22-day offensive on Gaza in December 2008, which left about 1,400 Palestinians and 13 Israelis dead.
Israel has a long history of assassination operations targeting militants. Most famously, in 1987 in Tunisia, agents killed Abu Jihad, the military leader of the Palestine Liberation Organisation.
But in 1997 one mission went wrong when two agents were arrested in Jordan after attempting to poison Mr Meshaal. Israel was forced by the US government to hand over an antidote.
More recently, Israel denied that it was behind the assassination of Imad Mughniyeh, the military commander of the Lebanese Shia militant group, Hezbollah, in Damascus in 2008.