Being on the list gives sites access to enhanced international assistance, both technical and financial, and helps mobilise the international community to ensure their protection.
Odesa, a strategic port city on Ukraine's Black Sea, was also added to the list.
The World Heritage Committee used an emergency procedure to add the ancient kingdom of Saba in Yemen's Marib province to the list, due to the threat of destruction from continuing conflict.
Yemen has been mired in a devastating civil war that began in 2014, when the Houthi rebels seized Sanaa and much of the north of the country.
The UN's cultural agency Unesco said on Wednesday that Yemen is home to a “serial property comprised of seven archaeological sites that bear witness to the rich kingdom of Saba and its architectural, aesthetic and technological achievements from the first millennium BCE to the arrival of Islam around 630 CE”.
The kingdom controlled much of the “incense route across the Arabian Peninsula, playing a key role in the wider network of cultural exchange fostered by trade with the Mediterranean and East Africa”, it added.
Yemen's ambassador to Unesco, Mohammed Jumeh, congratulated the Arab world on the listing.
“Congratulations to Marib, to Yemen, to the Arab region for this great cultural achievement, which was the fruit of three years of hard work and efforts,” Mr Jumeh said on Twitter.
Lebanon's Rachid Karameh International Fair of Tripoli was also added to the List of World Heritage in Danger.
“The World Heritage Committee used an emergency procedure to inscribe the site, due to its alarming state of conservation, the lack of financial resources for its maintenance, and the latent risk of development proposals that could affect the integrity of the complex,” said Unesco.
The site was designed in 1962 by the Brazilian architect Oscar Niemeyer on a 70-hectare site between the historic centre of Tripoli and Al Mina. It was intended to be a permanent world fair but construction stopped following the outbreak of the 15-year civil war in 1975 and today lies abandoned.
“The main building of the fair consists of a huge covered hall in the shape of a boomerang of 750 metres by 70 metres, a flexible space for countries to install exhibitions,” Unesco said. It added that it is known to be “one of the major representative works of 20th century modern architecture in the Arab Middle East".
Adding Odesa as a World Heritage in Danger site will give the city access to financial and technical international aid, following months of being under threat since Russia's invasion of Ukraine.
Odesa has been bombed several times by Russia since it invaded Ukraine on February 24, 2022.
In July last year, part of the large glass roof and windows of Odesa’s Museum of Fine Arts, inaugurated in 1899, were destroyed.
In a statement, Unesco Director General Audrey Azoulay said that Odesa, a “free city, world city, legendary port,” had made its mark on cinema, literature and the arts and was thus “placed under the strengthened protection of the international community.”
“As the war continues, this inscription reflects our collective determination to protect this city from greater destruction,” she added.