Haniyeh has been based in Doha since around 2019. Hamas' political office moved to the Qatari capital in 2012 after its previous office in Damascus, Syria, was closed.
Haniya played a key role in indirect negotiations with Israel over a potential ceasefire agreement in the war in the Gaza Strip.
The heads of the CIA, Mossad, Egyptian and Qatari intelligence agencies attended the negotiations in Doha.
Haniya's funeral caps a week of rising tensions in the Middle East following the deaths of 12 children and teenagers in an Israeli airstrike on the occupied Golan Heights.
Israel has blamed Hezbollah and vowed “severe” retaliation, but Hezbollah denies any involvement.
A few days later, a senior Hezbollah commander, Fuad Shukr, was killed in an Israeli airstrike in Beirut. Four others, including two children, were also killed.
Hours later, Ismail Haniyeh, a key Hamas supporter, was assassinated in Iran while attending the inauguration of Iran's new president, Masoud Fezeshkian.
Israel has not claimed responsibility for the assassination, but Israeli Prime Minister Benjamin Netanyahu later said Israel had struck a “significant blow” to Iranian proxy groups in recent days.
A senior Hamas official told the BBC that the killing took place in a building where Haniyeh had stayed during a previous visit to Iran. They said three Hamas leaders and several security guards were in the building with him.
The circumstances surrounding his death remain unclear.
Senior Hamas officials told the BBC that Haniya's killing had left the Hamas leadership “shocked”.
Senior Hamas official Khalil al-Haya told a news conference that the missile hit Haniyeh “directly,” citing witnesses who were present.
But the New York Times, citing seven government officials, reported that Haniyeh was killed by a bomb smuggled into the building where he was staying two months ago.
The BBC has been unable to verify these claims.
