The blockade of the Gaza Strip is putting residents' health at risk, the UN and aid groups have warned.

Medical facilities and equipment are in disrepair, many damaged in Israel's military operation a year ago have not been rebuilt, they said.

Some 27 patients died last year waiting to be referred out of Gaza, they said.

Israel and Egypt deny entry to all but basic humanitarian supplies, in order to prevent Gaza's Hamas rulers firing rockets at Israel, they say.

UN agencies and the Association for International Development Agencies (AIDA), which represents more than 80 humanitarian organisations, said the Israeli restrictions were "undermining the functioning of the health care system and putting at risk the health of 1.4 million people in Gaza".

Max Gaylard, the UN's humanitarian coordinator in Gaza, said the blockade was hampering the provision of medical supplies and the training of health staff.

He said it was also "preventing patients with serious medical conditions getting timely specialised treatment outside Gaza".

Some treatments, such as complex heart surgery and treatment for certain types of cancer, are unavailable in Gaza.

The agencies highlighted the case of 19-year-old Fidaa Talal Hijjy, who they say died while awaiting permission to leave Gaza for a bone marrow transplant she needed to treat Hodgkin's disease.

They said she had applied for permission three times to attend appointments at hospitals in Israel, but each time the Israeli authorities failed to respond in time and she missed the appointment.

Her request was approved the day after she died, on 11 November.

The World Health Organization says 88 people have died while waiting for permits since November 2007.

On average 20% of essential drugs were out of stock in Gaza between March and November 2009, according to WHO figures.

Israel allows most medicines into Gaza, but there have been problems with the supply chain.

Most Gazans are not allowed to leave the territory, and the agencies also said medical staff had generally been unable to travel out of Gaza to update their expertise.

Fifteen hospitals and 43 clinics were damaged or destroyed in Israel's operation in Gaza a year ago and most had not been rebuilt because constructions materials have not been allowed in, the agencies said.

The Israeli authorities are yet to respond to the aid agencies' statement.

However, in the past Israel has said extensive security screening is necessary for patients who wish to leave, as three people with permits to leave for medical reasons have been found to be planning attacks in Israel.

It has also said it has offered to facilitate passage through Israel to Jordan for Gazan patients it refuses permits to on security grounds.

Israel said the 22-day military operation, which began on 27 December 2008, was aimed at halting rocket fire by Palestinian militants into Israel.

It says the almost total ban on construction materials such as cement entering Gaza is because they may be used for building rockets, launch pads or weapons smuggling tunnels.

Israel tightened its blockade of the Gaza Strip in June 2007, after Hamas forced out the forces of its more secular rival Fatah, which the Islamic movement had beaten in elections the previous year.