Washington remained committed to pressing for a ceasefire between Israel and Hamas Tuesday despite Palestinian militants rejecting a short-lived truce and Israel resuming its deadly air campaign against Gaza.

U.S. Secretary of State John Kerry said as the Egyptian-drafted ceasefire plan was unveiled that he would be willing to return to the region at a moment's notice if it would help bring the parties to a truce.

An Israeli surveillance drone flew over the southern city of Tyre on Wednesday evening after several rockets were launched for the past four consecutive nights towards Israel from a region in the port city.

The state-run National News Agency reported that an “Israeli surveillance drone flew as of 8:50 pm in the southern region's airspace above Tyre.”

Palestinian health minister Jawad Awad cancelled a trip to Gaza City's Shifa hospital on Tuesday after being confronted by angry protesters as he arrived from Egypt, officials said.

Witnesses said protesters threw shoes and eggs at Awad's car as he entered Gaza through the Rafah border crossing.

The U.N. aid agency for Palestinians on Tuesday described the damage wrought by Israel's air offensive on Gaza as "immense", with more than 500 homes razed.

"The level of human losses and destruction in Gaza is really immense," said UNWRA spokesman Sami Mshasha.

Hamas allowed a group of 25 Palestinians, including those seeking medical treatment, to cross from Gaza into Israel after closing the border crossing earlier on Tuesday.

But it declined to let anyone else leave Gaza or enter from Israel, a Palestinian official in charge of coordinating movement at the Erez crossing told AFP.

U.S. Secretary of State John Kerry warned on Tuesday of the "great risks" of spiraling violence between Israel and the Gaza Strip and called on Arab nations to push Hamas to accept a ceasefire.

"There are great risks in what is happening there and the potential of an even greater escalation of violence," Kerry told reporters in Vienna, as he wrapped up two days of talks on Iran's nuclear program.

Turkish Prime Minister Recep Tayyip Erdogan on Tuesday stepped up his rhetoric against Israel over its deadly air offensive on Gaza, accusing the Jewish state of committing "state terrorism" against the Palestinians.

Presenting himself as the sole world leader speaking up for the Palestinians, Erdogan said that any normalization in the troubled ties between Israel and Ankara was currently out of the question.

U.S. President Barack Obama on Monday welcomed Egypt's proposal for a ceasefire between Israel and Hamas in Gaza, saying he hoped it could restore calm.

At an Iftar dinner marking the Muslim Holy month of Ramadan, Obama also said Israel had a right to defend itself against "inexcusable" rocket attacks but described the deaths of Palestinian civilians in the conflict as a "tragedy."

The United States on Monday warned against any Israeli ground invasion of Gaza, saying it would put even more civilians at risk than are currently in the crossfire of attacks on Hamas.

But the White House stopped short of criticizing Israel over the civilian toll so far in Gaza of the offensive, saying the government had a "right" and "responsibility" to defend their citizens against rocket attacks.

Washington's top diplomat is to head to the Middle East on Tuesday to throw his weight behind diplomatic efforts to end a devastating week-long conflict between ally Israel and its Islamist foe Hamas.

With Israel's punishing air campaign in its seventh day, the death toll in Gaza hit 177, prompting growing calls for a ceasefire which have so far showed little sign of progress.