A vessel bound for Iran had been loaded in the port of Yuzhny near the Black Sea port of Odessa, a trader said.
The previous shipments of maize to Iran were made in November 2012, when Ukraine, one of the world's top maize exporters, sent a total of 124,000 tonnes of the commodity, Mykola Vernytsky from ProAgro consultancy told Reuters.
"The suspension of shipments was likely to be caused by international sanctions as other countries in the region were continuing maize purchases without any pauses," Vernytsky said.
Ukraine's Agriculture Minister Mykola Prysyazhnyuk said this week that Ukrainian private companies were considering an increase in their food exports to Iran, despite payment problems caused by the sanctions.
He said that such shipments by private companies were already under way, adding that there were no barter deals with Iran but "direct payments".
The minister declined to give details of how Iranian consumers pay for Ukrainian produce.
The European Union and the United States have imposed toughened sanctions meant to discourage Tehran's nuclear programme, which they say has a military purpose. Iran rejects this.
Western sanctions do not target food shipments, but financial measures have frozen Iranian firms out of much of the global banking system, complicating payments for imports on which Iran relies for much of its food, consumer and industrial goods.
Many foreign companies, including shipping firms, have pulled out of trade with Iran for fear of losing business in the United States and due to the complexities of arranging non-sanctioned deals.
Ukraine, which plans to export about 14 million tonnes of maize this marketing year, sold 155,200 tonnes of maize to Iran so far the 2012/13 July-June season.
The former Soviet republic exported 1.7 million tonnes of maize to Iran in 2011/12.
