Two Iranian ships are stranded in Brazil because Brazil’s state-run oil company Petrobras refuses to sell them the fuel needed to return to Iran due to sanctions imposed against Iran by the United States.

Reuters explained on Friday that the cargo ships Bavand and Termeh arrived in Brazil a few months ago to deliver a shipment of petrochemical fertilizer and pick up loads of corn. The Bavand was loaded up with 50,000 tons of corn and the Termeh is supposed to take on another 66,000 tons.

Carrying food back to Iran is legal under U.S. sanctions and Iran buys a great deal of corn from Brazil, but unfortunately for the Iranian captains, the Petrobras subsidiary that sells maritime fuel in Brazilian ports cited the U.S. sanctions and refused to refuel the ships. The Iranian government might need to send a tanker loaded with fuel all the way to Brazil to get the cargo vessels and their loads of corn.

Reuters explained that, unlike most ships employed in Iran’s agricultural trade with Brazil, the Bavand and Termeh are both flying Iranian flags. Iranian-flagged vessels usually arrive in Brazil with enough fuel to make it home, but that evidently was not the case with these two ships.

Petrobras stated that both Iranian ships appear by name on a list of sanctioned vessels, so refueling them could “have consequences for the oil company,” as Radio Farda put it. Petrobras is listed on the New York Stock Exchange and has operations in the United States, making it vulnerable to secondary sanctions.

The Iranian state company that owns the ships, Sapid Shipping Company, is attempting to sue Petrobras subsidiary Transpetro for refusing to refuel the ships. Sources familiar with the case said these efforts have been unsuccessful thus far.

The Rio Times pointed out on Friday that at least one other Iranian ship appearing the sanctions list was able to load corn and return home, while another sanctioned vessel is scheduled to pick up a load in August. The report did not indicate whether the earlier ship purchased fuel in Brazil, or whether the ship due in August plans to do so.

“The case comes at a time when relations between Brazil and the U.S. are at their closest, with president Jair Bolsonaro seeking deeper ties with the country government by Donald Trump,” the Rio Times added.