Hamas interior minister Said Siam was killed in an Israeli air strike in the Gaza Strip, Hamas and U.S. Intelligence officials confirmed to FOX News Thursday.

Siam was in charge of 13,000 Hamas police and security officials, many of whom are involved in the Gaza conflict with Israel, Hamas-run television reported.

The news of Siam's death came as U.N. Secretary-General Ban Ki-Moon said that Israel was to make an important decision on a possible cease-fire in the Gaza Strip, Reuters reported.

"I understand today the Israeli government will make an important decision on a ceasefire. I hope that decision will be the right one," Ban told Reuters.

Also Thursday, Israeli tanks shelled downtown Gaza City and ground troops thrust deep into a crowded neighborhood for the first time, sending terrified residents fleeing for cover and increasing pressure on Hamas to accept a proposed cease-fire to end Israel's offensive.

The U.N. refugee agency also said its Gaza headquarters was struck by Israeli artillery fire and the building was ablaze.

The building was hit by what was believed to be three white phosphorous shells, spokesman Chris Gunness said. The weapons burn at extremely high temperatures and easily set fires.

A senior Israeli military officer said Israeli troops shelled the complex after coming under fire from Palestinian militants.

The artillery attack set the compound ablaze, destroyed tons of food and humanitarian supplies and forced hundreds of refugees to flee.

Gunness says the building had been used as a shelter for hundreds of people fleeing Israel's offensive. He said three people were injured.