Iran's once optimistic tourism industry has been left in disarray following the reintroduction of U.S. sanctions against Tehran in early August.

The move by President Donald Trump has led to tourists shying away from Iran, while locals are not spending their money either, both of which have had a negative effect on the country's economy.

Local businessman Jalal Rashedi, who owns six hostels, is doubtful that Iran will be able to attract overseas visitors and investors anytime soon.

"(We are) simply preparing for the dark storm clouds looming in the horizon," he told CNBC. "And they are coming, if you ask me. They come with the winter clouds."

Things were very different when the U.S., the U.K., France, China, Russia and Germany signed a nuclear accord with Iran in 2015. The agreement, officially called the Joint Comprehensive Plan of Action (JCPOA), saw international sanctions on Iran lifted in exchange for the country curbing its nuclear program.

The move brought Iran back into the international fold and resulted in a boom in tourism — $3.2 billion in 2014, $3.3 billion in 2015, $3.5 billion in 2016, before dropping to $2.8 billion in 2017, according to the World Tourism and Travel Council (WTTC) — with the widespread construction of new hotels and the refurbishment of existing ones. Tehran worked to boost this burgeoning tourism sector with a large injection of capital and setup a ministry of tourism.

This reintegration into the global community saw companies like French hotel giant Accor move into Iran. Accor opened an Ibis and a Novotel hotel in Tehran in 2015, becoming the first international hotel chain in the country since the Iranian Revolution in the late 1970s. Now that the JCPOA has seemingly fallen apart, Accor declined to comment on whether its hotels would stay open despite Washington's sanctions, or if its outlook on the country had changed.

Despite government efforts to limit the fallout from Trump's decision, economic uncertainty is widespread.

In August, British Airways and Air France followed KLM in announcing an end to direct flights to Tehran, citing a lack of interest in the route. Lufthansa, Austrian Airlines and Alitalia are the only European airlines still flying to Iran.

Alireza Miryousefi, spokesman for Iran's United Nations mission, told CNBC. he believed that "that other airlines, such as Iran Air, can fill the void."