LONDON, July 4 (Reuters) - British Prime Minister Boris Johnson said on Monday that alternative routes to retrieve grain stuck in Ukraine will need to be looked at, including through Europe's Danube river, if it cannot be moved via the Bosphorus strait in Turkey.
"The Turks are absolutely indispensable to solving this. They're doing their very best ... It does depend on the Russians agreeing to allow that grain to get out," Johnson told parliament.
"We will increasingly have to look at alternative means of moving that grain from Ukraine if we cannot use the sea route, if you can't use the Bosphorus."
Turkey said it has halted a Russian-flagged cargo ship off its Black Sea coast and is investigating a Ukrainian claim that it was carrying stolen grain.
Johnson told lawmakers that there were solutions that did not involve the presence of UK or other warships in the Black Sea.
"What we're also looking at is the possibility of using the river, using the Danube in particular, (or) by using the railways, to try to get the grain out in smaller quantities than we will be able to do with a giant convoy through the .. Black Sea," he said.
"We are looking at all the possible options." (Reporting by William James, writing by Muvija M, Editing by Alistair Smout)