Washington's top diplomat will discuss the Gaza war with Turkey's mercurial leader on Saturday before flying to Crete to address Greek worries about the looming sale of US fighter jets to Ankara.

US Secretary of State Antony Blinken arrived in Istanbul late Friday for the first leg of a trip that includes visits to Israel and West Bank, along with five Arab states.

Blinken's fourth crisis tour since the start of the Israel-Hamas war three months ago comes with fears mounting that the conflict will engulf swathes of the Middle East.

Istanbul served as a base for Hamas political leaders until Hamas fighters raided Israel, killing around 1,140 people and triggering a reprisal offensive that the Gaza health ministry says has claimed 22,600 lives -- most of them women and children.

Turkey asked the Hamas chiefs to leave after some were captured on video celebrating the deadliest attack in Israel's history.

But Turkish President Recep Tayyip Erdogan has since turned into one of the Muslim world's harshest critics of the scale of death and destruction happening in Gaza -- and of Washington's support for Israel. 

Erdogan has compared Israeli Prime Minister Benjamin Netanyahu to Adolf Hitler and accused the United States of sponsoring the "genocide" of Palestinians.

He has also rebuffed US pressure to cut off the suspected flow of funding through Turkey to Hamas and defended the group as legitimately elected "liberators" fighting for their land.

The US State Department on Friday announced $10 million rewards for information about five alleged Hamas foreign operatives -- three of them believed to be based in Turkey -- thought to be helping finance the Iran-backed group.

Turkey this week countered by detaining 34 people suspected of planning attacks against Palestinians and spying for Israel's Mossad intelligence agency.

NATO and F-16s

Erdogan began to tone down his most strident comments after US President Joe Biden last month called the Turkish leader for the first time since the war broke out.

The call helped push along NATO member Turkey's glacial progress in accepting Sweden into the US-led defence organisation in the wake of Russia's war on Ukraine.

A parliamentary committee approved Sweden's application in late December.

Blinken will hope to win assurances in talks with Turkish Foreign Minister Hakan Fidan and Erdogan that a vote by the full chamber will happen soon.

Approval from all NATO states is required for new members to join the defence bloc.

NATO has already doubled the length of its border with Russia when Turkey relented and accepted Sweden's neighbour Finland into the alliance last year.

Erdogan has been able to use Turkey's veto power to impel Sweden into taking a tougher stance with Kurdish group in Stockholm that Ankara views as "terrorists".

He has also been trying to make Sweden's approval conditional on the US delivering 40 US F-16 fighters jets and nearly 80 modernisation kits for Turkey's ageing air force.

Biden's administration officially backs the sale, but has been unable to overcome resistance in Congress from lawmakers who express alarm about Turkey's position on Sweden and its human rights record, as well as past military standoffs with historic rival Greece.

"We have made clear that we do not believe the sale... should be linked with Sweden's NATO accession, but there are members of Congress who have a different opinion and they have linked the two," State Department spokesman Matthew Miller said this week.

Blinken will travel to the Greek island of Crete on Saturday evening for talks with Prime Minister Kyriakos Mitsotakis.

Greece has fiercely resisted the US jet sales because of its longstanding territorial disputes with Turkey in the energy-rich eastern Mediterranean region.