Haniyeh, the Palestinian armed group's political chief, played a key role in mediated talks aimed at ending nearly 10 months of war in Gaza.

His killing triggered calls for revenge and raised questions about the continued viability of such negotiations.

Mourners lined up for funeral prayers inside Imam Muhammad bin Abdul Wahhab Mosque, the Gulf emirate's largest. Others prayed on mats outside in temperatures that reached 44 degrees Celsius (111 degrees Fahrenheit).

Draped in a Palestinian flag, his casket was carried briefly into the mosque before leaving again for burial in Lusail, north of the Qatari capital.

The killing of Qatar-based Haniyeh is among several incidents since April that have sent regional tensions soaring during the Gaza war which has drawn in militant groups in Syria, Lebanon, Iraq and Yemen.

Turkey and Pakistan announced a day of mourning on Friday to honour Haniyeh, while Hamas called for a "day of furious rage".

Many Doha mourners were dressed in crisp white traditional robes, others in street clothes. But most wore scarves that combined the Palestinian flag with a checkered keffiyeh pattern and the message in English: "Free Palestine".

Doha traffic police and Qatar's internal security forces monitored all approaches and police lined highway embankments adjoining the mosque grounds.

Iran's First Vice President Mohammad Reza Aref and Turkish Foreign Minister Hakan Fidan were among the officials due at the funeral.

Haniyeh and a bodyguard were killed in a pre-dawn "hit" on their accommodation in Tehran early on Wednesday, Iran's Revolutionary Guards said. Haniyeh was in Iran to attend the swearing-in of President Masoud Pezeshkian a day earlier.

Israel, accused by Hamas, Iran and others of the attack, has not directly commented on it.

A source close to Lebanon's Iran-backed Hezbollah movement told AFP that Iranian officials met in Tehran on Wednesday to discuss next steps with representatives of the "Axis of Resistance", Tehran-aligned Middle East groups that include Hezbollah and Hamas.

"Two scenarios were discussed: a simultaneous response from Iran and its allies or a staggered response from each party," said the source who had been briefed on the meeting and requested anonymity to discuss sensitive matters.

During the Gaza war, Hezbollah and Israeli forces have engaged in near-daily exchanges of fire, and did so again on Thursday.

The Hamas leader's assassination came hours after Israel struck a southern suburb of Beirut, killing Fuad Shukr, the military commander of Hezbollah which supports Hamas.

Israel "delivered crushing blows to all our enemies", said Prime Minister Benjamin Netanyahu.

In Tehran on Thursday, Iran's supreme leader Ayatollah Ali Khamenei led prayers for Haniyeh, having earlier threatened "harsh punishment" for his killing.

The New York Times, citing Middle Eastern officials, reported that Haniyeh was killed by an explosive device planted several weeks ago at a Tehran guesthouse.

Asked about the report, Israeli military spokesman Daniel Hagari told journalists "there was no other Israeli aerial attack... in all the Middle East" on the night of Shukr's killing in Lebanon.

Hugh Lovatt, an analyst at the European Council on Foreign Relations, said Haniyeh's killing, at the very least "will mean that a ceasefire deal with Israel is now totally off of the table".

Still, the international community called for calm and a focus on a Gaza truce -- which Haniyeh had accused Israel of obstructing.

Hezbollah chief Hassan Nasrallah, addressing the funeral of Shukr, said Israel and "those who are behind it must await our inevitable response" to the twin killings.

Israel said Shukr's assassination was a response to deadly rocket fire which killed 12 youths last week in the annexed Golan Heights