A Ukrainian pilot on trial in Russia over the killing of two journalists is due to make her closing statement in court after five days on hunger strike.
Nadia Savchenko denies directing artillery fire at the Russian journalists in June 2014.
She is reported to have refused all food and drink since her hearing was adjourned before she was given a chance to make her last statement on Thursday.
The EU and US have both called for her immediate release.
In a statement, US Vice President Joe Biden described Ms Savchenko as having been “unjustly imprisoned in Russia since 2014 – detained and facing trial on trumped up charges”.
She was captured in 2014 at the height of the fighting between Ukrainian troops and pro-Russian rebels.
The 34-year-old insists the whole case against her is politically motivated, and she has become a symbol in Ukraine of her country’s resistance against Russia.
She says she was kidnapped by rebel fighters at least an hour before the attack in which the two Russian TV journalists were killed.
A team of “the best Ukrainian doctors” are due to examine her on Wednesday amid concerns for her health, according to a Ukrainian lawmaker.
Ms Savchenko called her hunger strike to protest at what she has described as her “illegal imprisonment” in Russia and “farce” of a murder trial, reports the BBC’s Sarah Rainsford in the Russian town of Donetsk.
Whilst the defendant is weak, a Ukrainian diplomat who visited her on Tuesday told the BBC that she was still in “fighting spirit”.
The EU has expressed concern about Ms Savchenko’s wellbeing, and Nobel prize-winner Svitlana Aleksievich is among more than 4,300 signatories to an open letter urging European leaders to act to secure her freedom.
Relations between Russia and Ukraine – along with its Western allies – have deteriorated following Moscow’s annexation of the Crimea peninsula in 2014 and its support for pro-Russian rebels in eastern Ukraine.