LONDON, ENGLAND — U.S. sanctions on Iran have stranded 20 ships carrying about 1 million tonnes of grain outside of Iranian ports, Reuters reported, citing sources directly involved in the trade.

The renewed sanctions, which cover a wide range of products from oil to financial activities, have created payment problems and added costs to some of the world’s largest trading companies, the news agency said. The sanctions have deterred several foreign banks from doing any Iranian business.

Sources told Reuters that cargoes are being held up for more than a month outside of Bandar Imam Khomeini and Bandar Abbas, Iran’s biggest ports for goods.

The ships are carrying soybeans and corn, mostly from South America.

According to an Iranian port official, who did not want to be named, there have been problems since U.S. sanctions were imposed on Iran’s financial system in November 2018.

“What has changed is that now the number of banks, traders that are staying away from doing business with Iran is increasing,” the official told Reuters.

Bunge and COFCO International were among the grain companies impacted, the news agency said. COFCO declined to comment and a Bunge spokesman said, “While we don’t comment on or confirm commercial contracts, Bunge exports agricultural commodities in accordance with all applicable legislative frameworks.”

Other sources told Reuters that Archer Daniels Midland Co. (ADM) halted trading with Iran in August because of the increasing difficulties. An ADM spokeswoman declined to comment to Reuters.

Trade sources told Reuters in December that Bunge and Cargill as well as other suppliers had halted new food supply deals to Iran due to payment issues.

“In certain countries where international sanctions exist, we provide that food using the humanitarian exception for medicine and food,” Cargill said.