The Moscow City Court will hear arguments on August 16 in the case of six of the 24 Ukrainian crewmen detained in Russia, the TASS news agency has reported.
They, along with seven other sailors, have been ordered to stay in pretrial detention until October 24, while 11 others will be held until October 26.
A lower court prolonged their detention on July 17 as they await trial on charges of "trespassing" in what Russia claims are its territorial waters.
If found guilty, the sailors face up to six years in prison.
Russia has held the Ukrainian sailors since its forces fired on, boarded, and seized their vessels near the Kerch Strait on November 25.
The Kerch Strait is the sole passage from the Black Sea to the Sea of Azov. It runs between Russia and Crimea, the Ukrainian peninsula that Russia seized in March 2014 after sending in troops and staging a referendum deemed illegitimate by Kyiv, the United States, and at least 100 countries.
The takeover of the peninsula, and subsequent Russian support for separatist militants who seized parts of eastern Ukraine at the start of a conflict that has now killed some 13,000 people, came after pro-European protests pushed Moscow-friendly Ukrainian President Viktor Yanukovych from power in Kyiv.
Ukraine called the attack and capture of 24 crewmen a violation of international maritime law.
Western leaders have demanded that Russia release the crew, and the incident has led to the imposition of additional sanctions on Russia.
In May, the U.S. sanctioned six Russians, including at least two Federal Security Service officers and about a half-dozen defense firms, in coordination with the European Union and Canada.
Ukraine the same month won a favorable ruling from the Hamburg-based International Tribunal for the Law of the Sea, which ordered Russia to release all 24 sailors and the three impounded vessels.
In a resolution on July 18, the newly elected European Parliament called on Russia “to release without further delay and unconditionally all illegally and arbitrarily detained Ukrainian citizens both in Russia and in the temporarily occupied territories of Ukraine.”
The sailors were specifically mentioned in the nonbinding resolution.
In a March 12 report, the UN’s Office of the High Commissioner for Human Rights stated that Russia breached international humanitarian law and called the 24 captive Ukrainians "prisoners of war."