UNESCO has condemned the destruction of part of the Old City of Sanaa in Yemen by a Saudi airstrike.

The strike on Friday killed five people and destroyed three houses, laying waste to much of the World Heritage Site.

international outrage as #Saudis bomb UNESCO site in #yemen - but quiet on wider campaign of national ruination... pic.twitter.com/A8j11wvVWg — Jeremy Walker (@Jwalkerpress) June 12, 2015

Locals said it marked the first direct hit on old Sanaa since the Saudi-led coalition began their bombing campaign against Houthi militias in Yemen in late March.

AFP reported that the airstrike hit the Qassimi neighbourhood, which contains thousands of houses built before the 11th century.

Saudi sources, however, denied bombing the site, suggesting that stored Houthi weapons could be the cause.

"For sure we did not conduct any operation inside (the) city," Brigadier General Ahmed al-Assiri, the coalition spokesman, told AFP.

"Several days before they [Houthis] had an explosion in one of their storage" areas, he said. "So it could be one of these."

UNESCO on Friday expressed its alarm at the scale of the destruction.

“I am profoundly distressed by the loss of human lives as well as by the damage inflicted on one of the world’s oldest jewels of Islamic urban landscape,” said UNESCO’s director general, Irina Bokova.

“I am shocked by the images of these magnificent many-storeyed tower-houses and serene gardens reduced to rubble. This destruction will only exacerbate the humanitarian situation and I reiterate my call to all parties to respect and protect cultural heritage in Yemen. This heritage bears the soul of the Yemeni people, it is a symbol of a millennial history of knowledge and it belongs to all humankind.”

The Saudi-led coalition has stated its desire to see exiled former President Abd Rabbuh Mansour Hadi restored to power in Yemen and undermine what they see as Iranian-backed instability in the country.

The destruction wreaked upon the Old City of Sanaa, however, marks just the latest piece of Yemen's historical antiquities to be damaged in the fighting, coming less than two weeks after the Dhamar Regional Museum in the Hirran province of Yemen's Dhamar district was "completely destroyed" by Saudi airstrikes, according to the Khabar News Agency.

Writing for al-Araby al-Jadeed, journalist Abubakr al-Shamahi lamented the level of damage caused to Yemen’s ancient heritage by the Saudi-led bombing campaign.

“Dar al-Hajar, the rock palace that lies in a valley just outside Sanaa, was almost hit by missiles last week,” he wrote. “The Marib Dam, on the site of what locals say is the world's first ever dam, has been hit. The archaeological sites of the ancient civilisation that dam allowed to prosper, Sheba, have barely been uncovered from the sands. Yet even they have not escaped, with the Temple of Sheba, one of Yemen's national symbols, caught in the crossfire during the fighting in the area.

“Of course, the lives of the thousands killed in Yemen's war are more important. But I, and many other Yemenis, feel a deep sense of pain when we see the destruction of our heritage, places that we want to share with the world."