Hamas is regarded as a terrorist organisation by some countries
President Hosni Mubarak of Egypt has met Israeli Defence Minister Ehud Barak amid Egyptian efforts to broker a truce in Gaza between Israel and Hamas.
At talks in the Egyptian resort of Sharm el-Sheikh, Mr Barak warned that rocket fire from Gaza could spark a major Israeli military response.
He also insisted the release of captured Israeli soldier Gilad Shalit should form part of any truce.
Separately, the US criticised France for making contact with Hamas.
French Foreign Minister Bernard Kouchner confirmed his country had had recent contact with the Palestinian Islamist movement, which is officially regarded as a terrorist organisation by Israel, the US and the European Union.
The UK has said it believes France is committed to the EU position that there should only be engagement with Hamas if it abandons violence, recognises Israel and accepts previous Palestinian agreements and obligations.
A Hamas delegation has arrived in Egypt for talks with Egyptian officials on the group's offer of a six-month truce to Israel last week.
The delegation, believed to be drawn from members based in both Gaza and Syria, is due to meet Egyptian intelligence chief Lt Gen Omar Suleiman on Tuesday.
Hamas has already said the release of Gilad Shalit, captured in 2006, will not form part of any truce agreement with Israel.
Setting out Israel's conditions for a truce, Mr Barak said:
"We expect that if any kind of process toward reducing the level of violence will take place it will include a way to move toward his release."
There was no immediate comment from the Egyptians about President Mubarak's talks with the Israeli minister.
Criticising the French, a US state department spokesman in Washington said their move had not been "wise".
Mr Kouchner's comments followed quotes in the French media from a retired French ambassador, who said he had met senior Hamas officials about a month ago.
Last month, the Bush administration expressed displeasure at meetings between former US President Jimmy Carter and senior Hamas officials.
In France's defence, Foreign Minister Kouchner said that what was in question was "not relations [but] contacts" with Hamas.
"We are not charged with any kind of negotiation," he added.