Israel's recent easing of its blockade of Gaza is inadequate but shows restrictions could be lifted further without compromising the Jewish state's security, the top U.N. official in Gaza said on Thursday.

Israel tightened controls on the Palestinian territory three years ago after Hamas Islamists seized control there, but in recent weeks has allowed in some goods it used to ban, such as clothes and shoes, wood and aluminum.

John Ging, director of operations in Gaza for the U.N. Relief and Works Agency (UNRWA), welcomed the move but, quoting a comment by U.N. Secretary-General Ban Ki-moon during a visit to Gaza last month, called it "a drop in a bucket."

"A drop in the bucket is not a half-full glass," Ging told reporters in New York.

But, he said, the easing provided "practical proof ... that it can be done. So if we can have 25 truckloads of aluminum a month, then why not 50. And if you can have 50 then why not 100, and so on.

"The arguments that have been put forward to in some way excuse this blockade ... are now being of course undermined by these positive developments because ... it is now demonstrated that there are ways of overcoming the security challenges."

Aluminum is badly needed to make window frames in Gaza, which was heavily damaged in an Israeli assault on Palestinian militants in December 2008 and January 2009. Glass has been allowed in for some months, Ging said.

Israel continues to ban shipments of cement and steel to the Gaza Strip, where 1.5 million Palestinians live, on the grounds that Hamas could use them for military purposes.

The United Nations, which provides welfare and education to Palestinian refugees in Gaza and elsewhere through UNRWA, has repeatedly called for the blockade to be lifted.

Ging said that at the moment there was no "prospect of a restoration of the legitimate economy because there's no commercial trade into or out of the Gaza Strip."

The clothes and footwear that Israel has allowed into Gaza since April 4 at a rate of up to 10 container trucks a day have gone, however, to private Palestinian traders, who said this week they had begun ordering more from abroad. Previously the goods were allowed in mainly as part of aid shipments.

For the past three years, Gaza has been getting most of its consumer goods via tunnels from neighboring Egypt operated by smugglers who add on hefty surcharges.