Israel's siege of Gaza has turned the coastal strip into "a big open air prison," and continued international aid is needed to offer people there some hope, said a senior UN humanitarian official on Thursday.

"I would describe the situation as difficult and disappointing because very little has changed in the last year," John Holmes, UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator, said in an interview with Xinhua.

"It is a big open air prison, which is extremely depressing for the people who live there," he added.

Israel sealed off all crossing points with Gaza in 2007 after Islamic Hamas movement seized control of the coastal strip. Only limited quantities of medical humanitarian aid are allowed to enter the area since then.

Holmes told Xinhua that people in Gaza are suffering from high unemployment rate, food shortage and poverty. "Half the population is unemployed," he said, "if there is food in the shops people don't have money to buy it."

The UN official said he believed the most urgent problem is to launch the reconstruction plan, especially after most of the infrastructures and buildings were destroyed when Israel launched a military offensive in late 2008, allegedly to halt rocket fires from the area.

Holmes attributed the stalled reconstruction to the lockdown. "Gaza can't be reconstructed or redeveloped. Money is available from many donors, but it can't be used because you can't get the materials in to do it," he said.

Holmes toured Gaza and met with Israeli officials during his tour of region this week.

He said he was told by Israeli side that it's hard for Israel to lift the siege when Gilad Shalit, the Israeli soldier captured by Palestinian militants in 2006, is still held in Gaza.

"We don't think there is a link," said Holmes, adding that it is not acceptable or reasonable "to link the fate of one soldier with the fate of 1.5 million people in Gaza."

The UN humanitarian chief once again urged Israel to reopen the crossings and allow supplies in. Top priority should be building materials and machinery, he said, so as to help rebuilding houses and roads, repairing electricity and sewage system.

"It's a rather desperate, depressing situation where people are easily falling prey to despair," said Holmes. "That's not a good thing for the future of the people in Gaza, but also for the future of the peace process."

He appealed to the international community to continue relief efforts in Gaza, and help boost hope which is diminishing as time passes by.

"We can continue to provide the kind of humanitarian assistance that we have provided. I think it's very important that the people in Gaza don't feel forgotten by the international community," said Holmes.