Dubai police have implicated additional suspects in the killing of a Hamas military commander at a luxury hotel, as the country's police chief said he is all but convinced that Israel's Mossad spy agency is behind the assassination.

Mahmoud al-Mabhouh, a suspected high-level weapons smuggler who was a founder of Hamas' military wing, was found dead in the Al Bustan hotel on Jan. 20. The 50-year-old was reportedly suffocated with a pillow.

Al-Mabhouh was involved in the capturing and killing of two Israeli soldiers in 1989 and his brother said he had survived three previous attempts on his life.

Dubai investigators have concluded that al-Mabhouh's death came at the hands of a professional hit squad, which carried the fingerprints of a Mossad operation. They have released pictures of 11 suspects who travelled under Israeli names with bogus European passports, but sources with inside knowledge of the investigation say that an additional seven unnamed suspects were involved.

Lt. Gen. Dahi Khalfan Tamim spoke about the case to the Abu Dhabi government-owned newspaper The National, suggesting that Mossad is almost certainly the force behind al-Mabhouh's killing.

"Our investigators reveal that Mossad is involved in the murder of al-Mabhouh. It is 99 per cent, if not 100 per cent that Mossad is standing behind the murder," Tamim told the paper.

Tamim said that if it can be proven that the Mossad engineered the killing, Israeli Prime Minister Benjamin Netanyahu would be "the first to be wanted for justice" because he would have approved the assassination.

Israel has not admitted to taking part in al-Mabhouh's killing, nor has it denied being involved in his death.

"Israel never responds, never confirms and never denies," Foreign Minister Avigdor Lieberman told the government-owned Army Radio on Wednesday.

Meanwhile, a UAE official told The Associated Press that investigators now believe 18 people were involved in the Dubai operation.

The UAE official, who spoke anonymously, said two Palestinians are in custody and another five people -- including a woman caught on video surveillance at the hotel where al-Mabhouh's body was found -- are also suspects.

The official said some of the suspects used their passports to open U.S. credit card accounts.

After Dubai police initially released the names of 11 suspects earlier this week, media reports revealed that at least seven of the suspects shared names with real Israelis.

International security analyst Bob Ayers told CTV the fact that the passports had apparent links to Israel was an intriguing part of the story.

"They are putting the thought, for example, in your mind that Mossad would never be so obvious as to use passports that could be traced back to Israel. So you would think it's not Mossad, when it really was. It's a very, very interesting game of mirrors," Ayers said Wednesday.

Six of the suspects travelled with fraudulent British passports, while three others travelled with Irish passports. The other two suspects showed German and French passports, respectively.

But the fake passports have also caused controversy after the German, French, British and Irish governments have said they did not issue the passports shown to the world by Dubai police.

British Foreign Secretary David Miliband said one of his top diplomats had "explained the concern we have for British passport holders in Israel" during a meeting with Israeli Ambassador Ron Prosor.

"He made clear that we wanted to give Israel every opportunity to share with us what it knows about this incident, and we hope and expect that they will co-operate fully with the investigation," he said.

Irish Foreign Minister Micheal Martin said the three Irish passports had valid numbers, but different names than the names of the true passport holders.

With files from The Associated Press