CAIRO - NEW US peace envoy George Mitchell said on Wednesday it was critically important to consolidate the Gaza ceasefire, as Israel warned it would defend itself after a soldier was killed by Palestinian militants.

'It is of critical importance that the ceasefire be extended and consolidated. We support Egypt's continuing efforts in that regard,' he said after meeting Egyptian President Hosni Mubarak on the first leg of a Middle East tour.

Mr Mitchell, instructed by President Barack Obama to 'engage vigorously' to achieve real progress in the region, discussed with Mr Mubarak Egypt's efforts to bring peace to Gaza.

'The decision by President Obama to dispatch me to come to this region less than one week after his inauguration is clear and tangible evidence of this commitment,' Mr Mitchell said before leaving for his next stop, Israel.

Earlier on Wednesday, Israeli warplanes bombed tunnels under the border between Gaza and Egypt that Israel says are used to smuggle weapons, responding to an attack on Tuesday along the border that killed an Israeli soldier and wounded three others.

A Palestinian man was killed by Israeli fire shortly afterwards and a Hamas fighter and two other Palestinians were wounded in an air strike, also in southern Gaza.

'Israel wants the calm in the south to continue, but yesterday's deadly attack from Gaza was an attempt to deliberately undermine the calm,' government spokesman Mark Regev told AFP.

'In the face of such violent provocation, Israel will act to protect itself,' he said following the attack, which came 10 days after Israel and Hamas declared mutual ceasefires to end a deadly 22-day onslaught on Gaza.

The incidents marked the most serious violence since the unilateral ceasefires were declared on January 18, ending the Jewish state's war on the Islamist stronghold.

Ahead of Mr Mitchell's arrival in Egypt on Tuesday, Mr Obama said it was time for 'both sides to realise that the path that they are on is one that is not going to result in prosperity and security for their people.' 'Instead, it's time to return to the negotiating table,' he said in an interview with Al-Arabiya television.

Mr Mitchell started his mission in Egypt, a US ally that has played the central role in efforts to forge the fragile ceasefires in Gaza into a lasting truce.

Egypt has been holding separate talks with Israeli and Hamas officials, as well as with representatives of other Palestinian militant groups.

Mr Abul Gheit said the talks have 'evolved positively,' and that a 'permanent' Gaza truce could be agreed in the first week of February.

He said such a ceasefire would lead to the reopening of crossing points into Gaza, where most of the 1.5 million population depend on outside aid but have been suffering under a crippling Israeli blockade.

Hamas, which has said it is mulling an Israeli proposal for an 18-month renewable ceasefire, insists that Israel and Egypt open their crossing points into Gaza.

Israel has said it will not do so unless Hamas frees a soldier seized by militants in a cross-border raid in June 2006. Egypt has refused to permanently open its Rafah crossing in the absence of representatives of moderate Palestinian president Mahmud Abbas at the border.

Mr Abbas' Fatah faction and Hamas have been at odds since the Islamists ousted forces loyal to Abbas from the coastal strip in June 2007.

Israel's war in Gaza, launched on December 27 in response to militant rocket and mortar fire, killed more than 1,300 people, more than half of them civilians, and wounded more than 5,400, according to Gaza medics.

On the Israeli side, three civilians and 10 soldiers were killed in combat and by rocket fire.