Israel and the Gaza Strip's Hamas rulers remained firmly on a war footing today, despite a truce between the sides coming into effect.

Ehud Olmert, the Israeli Prime Minister, confirmed that his country's military was on high alert despite the ceasefire, and predicted that the halt in violence would be fragile and may be "short-lived".

"I think the strategy of Hamas, which does not want to recognise Israel’s right to exist in the first place, and the extremism, and the fanaticism, and the religious dogmatism, is the enemy of peace," Mr Olmert said, in an interview with an Australian daily newspaper today.

To illustrate the level of scepticism over the ceasefire, Israel this morning launched a military drill simulating an invasion in which 100 soldiers participated. The Israeli media saw the operation, at 5am local time, as a flexing of muscles.

Hamas, which seized control of Gaza last summer, was equally pessimistic that the deal would lead to calm, with a statement that the group was "fully ready to launch a military strike that would shake the Zionist entity if they did not abide by all the items of the calm".

Israel and Hamas have been locked in a war of attrition since last summer, with Israel staging a blockade on the territory as the Islamists continued to refuse to recognise Israel's right to exist or renounce terrorism.

The Egyptian-mediated truce comes as Mr Olmert embarks upon a flurry of diplomatic activity, including raising the prospect of a prisoner-swap with the Iranian-backed Lebanese Hezbollah guerrillas and carrying out indirect talks with Syria mediated by Turkey. Some of his many critics see this as part of the Prime Minister's efforts to defend his political position in the midst of a corruption investigation that could cost him his job.

Bashar al-Assad, the Syrian President, was today keeping his cards close to his chest over whether to hold his country's first top-level meeting with an Israeli Prime Minister at an economic summit to be attended by both countries in Paris next month.

"This is not like drinking tea," Mr Assad, in India on a four-day visit, said when asked if he would meet Mr Olmert.

He said that indirect Turkish-mediated talks would have to make more progress first. "The meeting between me and the Israeli Prime Minister will be meaningless without the technocrats laying the foundation, without reaching the final stage," he said.