"There is no proof Israel is involved in this affair, and if somebody had presented any proof, aside from press stories, we would have reacted," he said.
EU leaders have strongly condemned the murder and the use of forged European passports by assassins, but have not directly criticised Israel.
"The EU strongly condemns the fact that those involved in this action [assassination] used fraudulent EU member states' passports and credit cards acquired through the theft of EU citizens' identities," a declaration released on Monday said.
Martin said he told Lieberman of Ireland's "grave concern about the fraudulent use of passport material," with five Irish passports so far known to have been misused in
carrying out the assassination.
He said he told Lieberman that the security of Irish citizens had been placed at risk and that the theft, in this case of valid passport numbers, even if not names or photographs or credit cards, "violates the integrity of our passport system."
Although the EU is not directly responsible for passport issues, which are under the individual jurisdiction of its 27 members, it is likely to support any measures that the affected nations may propose.
A senior EU diplomat said Israel's suspected role in the murder of al-Mabhouh and the killers' alleged use of forged EU passports would threaten relations with the European bloc.
Separately, the British embassy in Israel said on Sunday it was giving new passports to six British nationals whose identities were stolen by the suspects.
Izzat al-Rishq, a Hamas official, told the Jordanian newspaper Al-Sabeel that the group "has formed a high-level investigation committee" to try to discover "how the Mossad was able to carry out the operation".
In Dubai, Anwar Gargash, the UAE's minister of state for foreign affairs, voiced concern on Sunday that the assassins used expertly doctored passports from nations that do not require advance UAE visas, allowing them to enter the country without scrutiny.
Sheikh Abdullah bin Zayed Al-Nahyan, the foreign minister, urged European allies to investiigate how fraudulent passports had been used by the hit squad.
Emirati officials close to the investigation said that at least two more suspects in the murder entered the country on fraudulent Irish passports.
They also said some of the 18 suspects visited the Gulf city state for a reconnaissance mission at least once before the murder.
The UK Sunday Times newspaper reported on Sunday that Binyamin Netanyahu, Israel's prime minister, had allegedly given the green light for the assassination.
The paper, citing "sources with knowledge of Mossad", said Netanyahu visited the Israeli intelligence headquarters in early January and, after being briefed, authorised the killing of al-Mabhouh.
A rehearsal of the operation, which reportedly involved at least 18 agents, was apparently carried out at a Tel Aviv hotel - without detection - prior to the briefing, The Times reported.
Hamas has acknowledged that al-Mabhouh smuggled weapons for it. The Palestinian group rules the Gaza Strip after seizing control from its rival Fatah in 2007. It is also opposed to Israel's existence as an independent state.