The civilians are taking shelter inside the Holy Family Church (file photo)
Civilians trapped in a church in Gaza City are living in an "unreal" sense of fear, a relative of one of those confined there has said.
Fifi Saba, whose sister is trapped inside the Holy Family Church, said people were scared to move out of fear of being shot.
Two women were killed inside the church by sniper fire on Saturday, the Latin Patriarchate of Jerusalem said.
Israel's army said it found no evidence its soldiers were involved.
Ms Saba, a Catholic from Gaza who now lives in the US, told BBC Radio 4's Today programme that she was worried about her sister, her brother-in-law and their two children aged 9 and 12, who were trapped there.
She said she was receiving news about them through a family member, who was able to speak to her sister once a day.
"They are locked in," she said. "They can't really see the street very much, and most of the time they're cut off from the world. They don't have their phones, they don't have internet, they don't have the news."
She said her sister often asked for news about what was happening outside, and was able to hear bombs overhead.
"The fear they have been living is unreal," she said.
Ms Saba said she received a message in which her sister said the "situation is really difficult".
"I found out later that day that when she said the situation is very difficult, she was witnessing the killing of the two people - the two women in the church," Ms Saba said.
Ms Saba added that the family had spent "a couple of hours" hiding on the ground in the church compound, because "they believed the Israelis were shooting anything that moves".
"They were terrified to go to the bathroom, because the women were shot trying to get to the toilet," she said, adding that the water to the church had been cut off for a few days.
Food was also scarce, she said, with those trapped living off boiled spaghetti for three weeks.
"And I think the past couple of days they have had no food," she said.
On Saturday, the Latin Patriarchate of Jerusalem said two Christian women - named as Nahida and her daughter Samar - were shot and killed while walking to a building in the church complex known as the Sister's Convent.
"One was killed as she tried to carry the other to safety," a statement said. Seven more people were shot and wounded as they "tried to protect others inside the church compound" on Saturday.
The patriarchate said no warning had been given and added: "They were shot in cold blood inside the premises of the parish, where there are no belligerents."
The patriarchate said that earlier on Saturday an Israeli tank fired on part of the church compound with 54 disabled people inside. It caused a fire that destroyed the building's generator, the only source of electricity, and some of the disabled people can no longer use their respirators, the statement said.
In response to the church's letter, the Israel Defense Forces (IDF), said it took "claims regarding harm to sensitive sites with the utmost seriousness".
It said that during dialogue between the IDF and "representatives of the community, no reports of a hit on church, nor civilians being injured or killed, were raised.
"A review of the IDF's operational findings support this."
The BBC has contacted the IDF for further comment on the accusations of indiscriminate shooting.
It is unclear why the church is allegedly being targeted, but Ms Saba said she did not believe Hamas fighters were inside, and that her sister had not mentioned their presence.
"We've seen in the past 72 days how hospitals are attacked, schools are attacked, libraries are attacked, markets are attacked, bakeries are attacked.
"I find it hard to believe if that's the narrative they're using," she said.
Layla Moran, a UK member of parliament, also told the BBC that members of her extended family, who are Christian Palestinians, were trapped in the church, having sought refuge after their home was bombed in the first week of the war.
"I'm now no longer sure they are going to survive until Christmas," she said, adding that they no longer had access to food or water.
The family members said soldiers had entered the church compound in the last 24 hours and had taken over a room in a building.
The family has sent a photo, seen by the BBC, of two bodies lying in a street outside the church building. Ms Moran's relatives say the bodies have been decaying for days.
Ms Moran said there had been no explanation as to why Israeli soldiers might target the church and no warnings or leaflets were sent to people sheltering there.
"It does feel like it's making a mockery of keeping civilians safe," she said.
Israel says it is carrying out military operations in Gaza to "eradicate" Hamas and rescue hostages taken by the group in its 7 October attacks. The Israeli military has repeatedly said it does not target civilians.
The Hamas-run health ministry in Gaza says more than 18,700 people have been killed and 50,000 injured in the enclave since the start of the war.