Mourners gathered at a Qatari mosque on Friday to bid farewell to Hamas leader Ismail Haniyeh, who was killed in Tehran in an attack blamed on Israel.
The assassination has heightened fears of a broader conflict.
Haniyeh, the political chief of the Palestinian group, played a key role in negotiations aimed at ending nearly 10 months of conflict between his group and Israel in Gaza.
His death has sparked calls for revenge and cast doubt on the future of such peace talks.
Haniyeh, who lived in Doha with other members of the Hamas political office, will be buried in Lusail, north of the Qatari capital, after funeral prayers at Imam Muhammad bin Abdul Wahhab Mosque, the Gulf emirate's largest.
His killing is among several incidents since April that have heightened regional tensions during the Gaza war, which has involved Iran-backed groups in Syria, Lebanon, Iraq, and Yemen.
Türkiye and Pakistan declared a day of mourning on Friday to honor Haniyeh, while Hamas called for a "day of furious rage."
Hours before the prayers, hundreds of mourners had already arrived at the Doha mosque.
Most wore scarves bearing the Palestinian flag or traditional keffiyeh patterns for the ceremony, held under tight security.
Doha traffic police and Qatar's internal security forces monitored all approaches, with police lining highway embankments adjoining the mosque grounds.
Haniyeh and a bodyguard were killed in a pre-dawn "hit" on their accommodation in Tehran early Wednesday, Iran's Revolutionary Guards said. Haniyeh had traveled to Iran to attend Tuesday's swearing-in of President Masoud Pezeshkian.
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 Agence France-Presse (AFP) that Iranian officials met in Tehran on Wednesday to discuss next steps with representatives of the "Axis of Resistance," Tehran-aligned groups in the Middle East 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 requested anonymity to discuss sensitive matters.
During the Gaza conflict, Hezbollah and Israeli forces have engaged in near-daily exchanges of fire and did so again on Thursday.
The Hamas leader's assassination came just hours after Israel struck a southern suburb of Beirut, killing Fuad Shukr, the military commander of Hezbollah, which supports Hamas.
Haniyeh's deputy, Saleh al-Aruri, had already been killed in south Beirut earlier this year in a strike that a U.S. defense official said Israel carried out.
In another high-profile killing, Israel's army on Thursday confirmed that an airstrike in July killed the Hamas military chief Mohammed Deif in Gaza.
Israel "delivered crushing blows to all our enemies," said Prime Minister Benjamin Netanyahu.
In Tehran on Thursday, thousands of mourners paid their respects during a public funeral ceremony for Haniyeh.
Iran's Supreme Leader Ayatollah Ali Khamenei led the prayers, having earlier threatened "harsh punishment" for his killing.
Haniyeh's coffin was then transferred to Doha. Iran's First Vice President Mohammad Reza Aref left Tehran to attend the ceremonies in Doha, the Iranian government announced on Thursday.
Netanyahu has vowed to destroy Hamas in retaliation for its Oct. 7 incursion on Israel that ignited the war in Gaza.
That attack resulted in the deaths of 1,197 people.
Hamas also seized 251 hostages, 111 of whom are still held captive in Gaza.
Israel's retaliatory campaign against Hamas has killed at least 39,480 people in Gaza.
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 spokesperson Daniel Hagari told journalists that 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 cease-fire deal with Israel is now totally off the table."
Still, the international community called for calm and a focus on securing a cease-fire in Gaza, which Haniyeh had accused Israel of obstructing.
U.S. President Joe Biden said he was "very concerned" about rising tensions in the region and added that Haniyeh's killing had "not helped" the situation.
The White House said Biden spoke with Netanyahu by telephone on Thursday, promising to defend Israel's security "against all threats from Iran."
"We have the basis for a cease-fire. He should move on it and they should move on it now," Biden told reporters after the call.
In Israel, hundreds of Israelis again marched in Tel Aviv to demand Netanyahu's government reach a deal that would bring home the remaining hostages.
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.
"You do not know what red lines you crossed," Nasrallah said, addressing Israel.
Israel said Shukr's assassination was a response to a deadly rocket fire that killed 12 youths last week in the annexed Golan Heights.
