May 17 (Reuters) - Russia's oil pipeline monopoly Transneft has limited access to monthly crude export loading schedules from Russian ports in a move to protect the country's oil market as tensions between Moscow and the West escalate, four sources familiar with the matter said on Tuesday.

Russian oil exporters will be provided only with the loading dates of their own cargoes instead of the standard practice of agreeing a document that included full loading plans for all exporters, they added.

The move is the latest instance of the Russian government withholding important statistical data from the market. In April the Energy Ministry limited access to its statistics on oil and gas production and exports.

The loading schedule for June 1-5 would have been issued by now, but this time traders were told that there is nothing to wait for, the sources said.

The document is normally put together based on Russian oil companies' requests and issued by Transneft. The loading schedules are issued for the Baltic Primorsk and Ust-Luga ports, the Black Sea's Novorossiisk and the Far East Kozmino ports.

Transneft did not immediately reply to a Reuters request for comment.

Transneft didn't used to publish the monthly loading plans from Russian ports on public platforms, but it did provide them to a wide range of interested market participants. In June, however, even oil companies won't have access to the full loading plan, the sources said.

The loading plans are crucial for participants in the Russian oil market including shippers, insurers and buyers of the oil, traders said.

"It is really difficult to work with so much data under wraps," a source at a non-Russian company involved in Russian oil trading said. "We feel blind."

Another source at a European oil company said that since that company had stopped active trading with Russia, it didn't really matter if it doesn't see the full loading schedule anymore. (Reporting by Reuters; Editing by Susan Fenton)