At least 30 Palestinians were killed in the first day of Israel's ground operation in Gaza, medics said on Friday.

Most of the more than 270 people killed in Gaza during Israel's 11-day offensive have been civilians, and around a quarter of them children. Israel has launched more than 2,000 airstrikes in the occupied territory, which was followed by volleys of tank fire and clashes with Palestinian fighters after the ground offensive began.

Israel says the military campaign is aimed at stopping Hamas rocket fire across the border and destroying militant group's network of tunnels. One Israeli soldier was killed in the ground fighting, and an Israeli civilian was killed earlier this week.

The Israeli army would not confirm the number of soldiers participating in the operation. The government has so far called up 66,000 reserve soldiers and more than 18,000 so far have received orders.

Number of displaced 'almost doubles'

The UN agency for Palestinian refugees, UNRWA, said that the number of displaced Gazans since Israel began its offensive has almost doubled in the past 24 hours to 40,000.

"The number of people coming to UNRWA seeking sanctuary from the fighting in Gaza has nearly doubled today. It has risen from 22,000 to over 40,000," said agency spokesman Chris Gunness.

"We are accommodating them in 34 UNRWA shelters," he added, saying the agency has launched an appeal for $60 million (44 million euros) to cover the cost of sheltering the displaced Gazans over the next month, and for other emergency measures until the end of the year.

US 'deeply concerned'

Speaking to reporters in Washington on Friday, US President Barack Obama said he had spoken by telephone with Israeli Prime Minister Benjamin Netanyahu and expressed his "deep concern" over the military escalation in Gaza.

However, Obama underscored the US position that Israel does have a right to defend itself.

dr/hc (AFP, dpa, AP, Reuters)