Staring straight ahead and rocking steadily backwards and forwards in her hospital bed, Sabah Abu Halima lists the fate of each of her nine children.

"Abed, 14 years old, was decapitated," she says. "Shaheed, one year and three months, was in my arms when the fire took her…"

Sabah explains that her husband and four of her children died when their house in northern Gaza was shelled during the recent Israeli offensive.

Many of the rooms in that house now lay dark and empty - blackened by fire.

The light fittings and power sockets have melted down the walls.

A shaft of light coming from the ceiling of the corridor, and mangled steel, marks the entry point of one of the missiles.

Scrawled, in Arabic, on the wall of a bedroom is the statement: "From the Israeli Defence Forces, we are sorry."

But on the next wall, there is a patch of white where, Sabah's 20-year-old son Mahmoud tells us, had also been the words "nice underwear". He says he scrubbed them off in anger.

'Strange burns'

Hundreds were killed in the 22-day Israeli offensive, but it is the manner in which Sabah's relatives lost their lives, and the weapon used, that has attracted attention.

Sabah herself has suffered terrible burns on her arms, legs and torso and is considerable pain.

"There was fire, and so much white smoke," she says. "The missile melted my children. My daughter-in-law melted in front of my eyes."

Dr Nafiz Abu Shabaan, the head of the unit in which Sabah is being treated, says he has seen many victims with what he described as "strange burns".

"These burns were very severe, very deep, and became deeper and wider over time," he says. "In some cases, smoke came out of the wound, even after hours."

The cause of these types of injuries is believed, by visiting medical officials, to be Israel's use of shells containing white phosphorus.

Incendiary weapon

In another part of the city, at a former security compound flattened by the Israeli bombardment, Marc Garlasco, senior military analyst at Human Rights Watch, points out evidence that white phosphorus had been used.

"We're standing here right next to an M825A1, which is the US designation for their white phosphorus shell," he says.

"Manufactured in the US and sold to Israel, the shell here is unexploded, although it's cracked and you can see the phosphorus pouring out in kind of this yellow-orange colour."

"Around the area there are also some white phosphorus felt pieces," he adds.

"As the weapon explodes in mid-air, 116 pieces of felt doused in white phosphorus fall on a large area. These pieces are littered around here. If you kicked them open, they would begin to smoke and potentially reignite."

Controversial as it is, white phosphorus is not illegal, at least in an open battlefield setting, where it is used to mask troop movements, or set on fire areas of high brush that need clearing.

But the international convention on the use of incendiary weapons says it should not be used where there is a possibility of hitting civilians.

The compound sticks to human skin and will burn right through to the bone, causing death or leaving survivors with painful wounds which are slow to heal.

United Nations officials say it was used in the shelling of a school in which hundreds of civilians were taking refuge from the fighting, and fired at the UN's main headquarters in Gaza.

Eyewitnesses and victims talk of it being used on many other occasions in built-up areas.

Internal investigation

After initially denying that white phosphorus shells were fired in Gaza, some Israeli military officials have now acknowledged its use.

The army says it has started an internal investigation, the insistence being until now that no weapons were used illegally.

Human rights groups have meanwhile started their own research.

"It's important that we investigate the use of white phosphorus, because it does appear that it was used incorrectly in a clear breach of Geneva Conventions, " says Mr Garlasco.

"But as grave as the injuries caused by white phosphorus are, there are a number of weapons that were used in Gaza that killed and injured an awful lot more people," he adds.

"We have to look at the full variety of weapons that were used here, how they were employed and how they impacted on the civilian population."