"The 80-meter bulk carrier, SNP Pazar, had engine trouble while sailing through the Bosphorus near the Fatih Sultan Mehmet Bridge, causing a pause in transit through the strait in both directions," the source said.
Ship trackers show that the vessel was en route to the Greek port of Kalymnos.
The source said that coast guard boats were trying to tug SNP Pazar away to unblock the crucial waterway, which connects the Black Sea to the Sea of Marmara and via the Dardanelles to the Mediterranean.