* Court freezes assets including stake in Detsky Mir
* Sistema sold part of Detsky Mir stake earlier on Tuesday
* Other seized assets include bank, agriculture unit (Recasts with court freezing on Sistema assets; updates shares)
MOSCOW, Dec 12 (Reuters) - A Russian court on Tuesday froze around $1.7 billion of conglomerate Sistema's assets at the request of oil major Rosneft, the TASS news agency reported.
State-controlled Rosneft had said earlier it was seeking to freeze some of Sistema's assets as part of a second lawsuit over Rosneft's Bashneft unit.
The arbitration court of Bashkortostan froze Sistema's 52.09 percent stake in toy retailer Detsky Mir, with a book value of 33.8 billion roubles ($571 million), TASS reported, citing a court decision.
Sistema's stake in Detsky Mir was due to fall to 47.1 percent as a result of a share sale on Tuesday. It was not immediately clear whether the injunction will prevent the deal from closing.
The court ruling was listed in an official legal database which showed that the court had taken a decison in response to a claim by Rosneft. No further details were available.
Sistema and Rosneft did not immediately respond to requests for comment. Earlier on Tuesday, Sistema rejected the asset freeze demands as groundless, saying Rosneft was pursuing a policy of blackmail aimed at destroying the company's value.
The court also froze Sistema's 90.5 percent stake in the Steppe agricultural holding worth 17.2 billion roubles, a 71.87 percent stake in MTS-Bank worth 15.3 billion roubles, 100 percent of Sistema Telecom Assets worth 8.7 billion roubles, a 16.18 percent stake in pulp and paper producer Segezha, and a number of other assets, TASS said.
The total book value of the assets frozen on Tuesday stood at around 99 billion roubles, TASS said.
The injunction prevents Sistema from disposing of the assets and from receiving income from the frozen shares.
Rosneft's demands came days after Sistema countersued Russia's top oil producer for around $5.6 billion, retaliating against $4.5 billion in legal claims made by Rosneft.
"The assets with which the earlier lawsuit was secured do not cover the damages under the second claim," Russian news agency RIA quoted a Rosneft spokesman as saying on Tuesday.
Rosneft filed its second 131.6 billion rouble lawsuit against Sistema in the arbitration court of Bashkortostan last week. The court scheduled preliminary hearings for Jan. 12, court documents showed on Tuesday.
The Russian government seized Sistema's stake in Bashneft in 2014, saying its privatization had been illegal. Rosneft later bought a controlling stake in Bashneft and in May filed its first lawsuit, alleging that Sistema had removed assets from the company. Sistema denies the allegation.
In August, the court ruled that Sistema should pay more than 136 billion roubles to Rosneft. As part of that lawsuit, the court seized 31.76 percent of shares in Sistema's MTS, Russia's top mobile phone operator, as well as 100 percent in the Medsi healthcare unit and 90.47 percent of power grid company BPGC. Sistema has lost appeals against the asset freeze.
Sistema, which holds the assets of Russian businessman Vladimir Yevtushenkov, has lost a quarter of its market value since the first lawsuit was filed in early May.
Sistema's London-listed stock was 0.27 percent lower by the market close on Tuesday at $3.66 per global depository receipt. ($1 = 59.2249 roubles) (Reporting by Anastasia Teterevleva, Maria Kiselyova, Katya Golubkova and Andrew Osborn; Writing by Maria Kiselyova; Editing by Gareth Jones and David Evans)