KYIV, Oct 25 (Reuters) - Ukraine's grain exports have fallen to 8.56 million metric tons so far in the 2023/24 July-June marketing season, agriculture ministry data showed on Wednesday.

The ministry gave no direct comparative data, but said that by Oct. 28 last year, Ukraine had exported 12.34 million tons of grain.

The exported volume this season included 4.28 million tons of wheat, 3.49 million tons of corn and 664,000 tons of barley. In the previous season Ukraine exported 4.7 million tons of wheat, 6.6 million tons of corn and 1.05 million tons of barley.

The ministry said 1.81 million tons of grain were exported in the first 24 days of October. Ukraine exported 3.65 million tons from Oct. 1-27 a year ago.

The ministry gave no explanation for the decrease, but traders and farmers' unions have said blocked Ukrainian Black Sea ports and Russian attacks on Ukrainian ports on the Danube River are the main reasons for lower exports.

Ukraine has traditionally shipped most of its exports through its deep water Black Sea ports.

Brokers said on Wednesday Ukrainian agricultural shipments via road routes had risen slightly so far this month as the country works to export as much as possible of its bumper grains and vegetable oil output this year.

A deal brokered by the United Nations and Turkey allowing such exports collapsed in July when Russia withdrew, saying its demand that sanctions be lifted on its grain and fertiliser exports had not been met.

Ukrainian officials said about 40 cargo vessels had entered a new Black Sea shipping corridor since it came into operation in August as Kyiv steps up a push to defy the de-facto Russian blockade.

Farm minister Mykola Solsky said about 700,000 tons of grain have been exported through the new corridor since it opened.

Ukraine can also export limited volumes through small river ports on the Danube and via its western land border with the European Union.

Ukraine's government expects it to harvest 79 million tons of grain and oilseeds in 2023, with its 2023/24 exportable surplus totalling about 50 million tons. (Reporting by Pavel Polityuk; Editing by Jan Harvey)