Nadia Savchenko, 34, is on trial for alleged involvement in the death of two Russian state television journalists in a mortar attack that came two months after Ukraine's pro-Moscow eastern revolt broke out in April 2014.
She faces up to 23 years in prison if convicted in a case that has drawn global attention and been attended by Western monitors concerned about Russia's record on human rights.
Savchenko denies the charges and has refused all food and drink since her hearing was adjourned last Thursday before she was given a chance to make a final statement.
Around 300 protesters gathered outside the Moscow mission holding up banners reading "(Russian President Vladimir) Putin will not break us" and "#FreeSavchenko" -- the Twitter hashtag used by her supporters worldwide.
"The Kremlin thought that this woman will submit to it and that it would thus be able to dictate its conditions to Ukraine," pensioner Volodymyr Marushchak told AFP.
"But Ukraine will remain free as long as it has people like Savchenko."
The pilot's case is seen by many Ukrainians as a symbol of resistance against what Kiev's pro-Western leaders view as Russia's aggression in the eastern industrial heartland of the former Soviet state.
The Ukrainian conflict has claimed the lives of more than 9,100 people and plunged Moscow's relations with the West to a post-Cold War low.
Russia rejects Ukrainian and Western charges of instigating and backing the unrest.
'Save My Child'
US Vice President Joe Biden added his voice to concern expressed by the European Union on Monday about Savchenko's fate.
"Nadiya has been unjustly imprisoned in Russia since 2014 -- detained and facing trial on trumped-up charges," Biden said in a statement issued today.
"Her unlawful continuing detention is a clear violation of Russia's commitment under the Minsk agreements, and she should be freed at once," he added in reference to a deal signed in the Belarussian capital aimed at ending Ukraine's separatist war.
The European Union described her hunger strike as "extremely worrisome".
"Russia bears responsibility for the health, well-being and observance of the human rights of all persons it detains," an EU spokeswoman said.
Prosecutors argue that Savchenko helped Ukrainian forces direct fire at the two Russian journalists in the separatist region of Lugansk.
She counters that she was in the area of the attack incidentally and was kidnapped and smuggled into Russia.
Savchenko's supporters fear that her refusal to drink may irreparably damage her health or even kill her before her next hearing on Wednesday.
A Ukrainian lawmaker from President Petro Poroshenko's party said a team of doctors would leave on Tuesday for the southern Russian detention centre where Savchenko is being held.
"Ukrainian diplomats have been able to wrest an agreement from the Russian authorities to allow our doctors to see (Savchenko) on March 9," Iryna Gerashchenko wrote on Facebook.
Savchenko's Russian attorney said that a check by Ukrainian officials today had shown "no visible deterioration" in his client's health.
"Savchenko is firmly determined to make her court statement on Wednesday," Nikolai Polozov wrote on Facebook.
But Savchenko's 78-year-old mother said she feared that her daughter had just days to live.
"I am so nervous, I forgot what it is like to sleep," Maria Savchenko said in a video statement issued on Monday.
"I appeal on world leaders to save my child."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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