"The heritage of Yemen is unique, reflecting centuries of Islamic thought, rich exchange and dialogue," UNESCO director general Irina Bokova said in a statement.
"I call on the people of Yemen, as well as on countries in the region engaging in military operations in Yemen, to do all they can to protect Yemen's invaluable cultural heritage."
Fear for the safety of archeological and cultural relics in Yemen has risen as a rebellion by Shiite fighters allied with Iran against government forces of President Abedrabbo Mansour Hadi has escalated into a regional conflict, with Saudi Arabia launching a campaign of air strikes Thursday in support of the regime.
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Among Yemeni sites on UNESCO's Intangible Cultural Heritage of Humanity list that are at risk is the old city in the capital Sanaa, whose mosques and rammed-earth tower houses date back to the eleventh century.
"Experience shows that cultural heritage is never more vulnerable than during times of conflict. It is crucial that all parties refrain from targeting, by shelling or by air strikes, or using for military purposes cultural heritage sites and buildings," Bokova said.
"The cultural heritage of a nation is essential for its citizens to preserve their identity, to benefit from their diversity and their history and to build themselves a peaceful future."
Formerly called Arabia Felix (Flourishing Arabia), Yemen is also home to the historic town of Zabid in the west, and the walled-city Shibam in the east, once known as "Manhattan of the desert" for its ancient seven-story high dwellings.