Hamas' top leader, Ismail Haniyeh, was buried in Qatar on Friday following his assassination in Tehran, the Iranian capital. His potential successor told mourners that his death would only make the Palestinian militant group more determined in its struggle against Israel.

Haniyeh's death was one in a series of killings of senior Hamas figures as the war between Hamas and Israel in Gaza nears its 11th month, with growing concern that the conflict is spreading across the Middle East.

Both Hamas and Iran have accused Israel of carrying out the assassination and have pledged to retaliate against their foe. Israel has not claimed responsibility for the death nor denied it.

Haniyeh was laid to rest in a cemetery in the city of Lusail after a funeral ceremony at the Imam Mohamed Ibn Abd Al-Wahhab Mosque in Qatar's capital, Doha.

His coffin, draped in the Palestinian flag, was carried in a procession past hundreds of people, alongside the casket of his bodyguard, who was also killed in the same attack in Tehran on Wednesday.

Mourners at the ceremony included Khaled Meshaal, who is tipped to be the new Hamas leader. Other senior Hamas officials and Qatar's Emir Sheikh Tamim bin Hamad al-Thani also attended.

Speaking at the mosque, where prayers were held over Haniyeh's body, Meshaal said his death would only make the group more determined to continue its fight for a free Palestine. There would be no concessions over its principles and no recognition of Israel, he said.

"Palestine will remain from the river to the sea...and the Zionists (Israel) have no place on the land of Palestine, regardless of how many they kill of us," Meshaal said in a video released by Hamas.

Haniyeh's death was a big loss to the movement, but it would not alter their course, he said.

"Our enemies don't learn the lesson, they have been killing our leaders for over 100 years, what happened? When a leader ascends (to heaven), another leader comes," he said.

Senior Hamas official Sami Abu Zuhri told Reuters by phone: "Our message to the occupation (Israel) today is that you are sinking deep in the mud and your end is getting closer than ever. The blood of Haniyeh will change all equations."

Haniyeh was killed by a missile that hit him directly in a state guesthouse in Tehran where he was staying, senior Hamas official Khalil Al-Hayya said in Tehran.

The strike was one of several recent hits that have killed senior figures in Hamas or the Lebanese movement Hezbollah in a conflict that is now stretching from Gaza to the Red Sea and the Lebanon-Israel border and beyond.

In the United States, U.S. President Joe Biden said Haniyeh's killing was not helpful to international efforts to secure a ceasefire in the war in Gaza.

"It doesn't help," Biden told reporters on Thursday, when asked if the action ruined the chances of a truce.

Qatar has been leading the peace effort along with Egypt and the United States, Israel's main ally.