WRAPUP 8-Ukrainian rockets hit Russian-held area as Kyiv readies southern counter-attack

(Adds updated injury toll reported in Nova Kakhovka, details on grain shipments)

* Ukraine strikes Russian-controlled Kherson region

* Says it kills 52, destroys hardware

* Russian-backed official reports civilian casualties too

* Says at least seven people killed

* Ukraine planning counter-offensive to retake south

By Tom Balmforth and Pavel Polityuk

KYIV, July 12 (Reuters) - Ukraine said on Tuesday it had carried out a long-range rocket strike against Russian forces and military equipment in southern Ukraine, territory it says it is planning to retake in a counter-offensive using hundreds of thousands of troops.

The strike hit an ammunition dump in the town of Nova Kakhovka in the Kherson region and killed 52 people, Ukraine's military said. It came after Washington supplied Ukraine with advanced HIMARS mobile artillery systems which Kyiv says its forces are using with growing efficiency.

The town's Russia-installed authorities gave a different version of events. The Russian TASS news agencies reported they said that at least seven people had been killed in the attack and around 70 injured. A Russian-backed official in Kherson said at least seven people had been killed and that civilians and civilian infrastructure had been hit.

Reuters could not independently verify the battlefield accounts.

The area Ukraine struck is one that Russia seized after launching on Feb. 24 what Moscow called "a special military operation" in its fellow ex-Soviet neighbour and is of strategic importance with Black Sea access, a once thriving agricultural industry and a location just north of Russian-annexed Crimea.

Ukrainian government officials have spoken of efforts to marshal up to a million troops and of their aim to recapture southern parts of the country now under Russian control.

"Based on the results of our rocket and artillery units, the enemy lost 5️2 (people), an Msta-B howitzer, a mortar and seven armoured and other vehicles, as well as an ammunition depot in Nova Kakhovka," Ukraine's southern military command said in statement.

Unverified videos posted on social media showed smoke and sparks, followed by an immense fireball erupting into the night sky. Images released by Russian state media showed a wasteland covered in rubble and the remains of buildings.

An official from the Russian-backed local administration said that Ukraine had used HIMARS missiles and that they had destroyed warehouses containing saltpetre, a chemical compound which can be used to make fertilizer or gunpowder. A large explosion resulted. Russia's TASS news agency reported later that the fires were extinguished.