Russia has said its support for Syrian president Bashar al Assad is "not unconditional" in the wake of a suspected chemical weapons attack that has provoked widespread condemnation.
The comment from President Putin's spokesman Dmitry Peskov comes after the Russian leader said it was unacceptable to make "groundless" accusations over the attack.
Tuesday's attack in Khan Sheikhoun in Idlib province killed more than 80 people, including up to 30 children , according to the British-based Syrian Observatory for Human Rights monitoring group.
Mr Putin defended the Syrian government during a telephone conversation with Israeli Prime Minister Benjamin Netanyahu on Thursday.
A statement issued by the Kremlin said the Russian President had "highlighted that it was unacceptable to make groundless accusations against anyone without conducting a detailed and unbiased investigation".
During the call, Mr Putin and Mr Netanyahu are said to have shared "an exchange of opinions over the incident with chemical weapons".
Israel has joined a chorus of Western allegations that Assad's forces were behind the suspected chemical attack.
Britain, France and the US have asked the UN Security Council to hold a vote later on Thursday on a draft resolution demanding an investigation.
Russia has said it is too early to blame the Syrian government and has also called for an investigation, although it is unclear whether Moscow will support the resolution.
Officials from the World Health Organisation in the southern province of Adana, together with officials from Organisation for the Prohibition of Chemical Weapons (OPCW), are currently collecting evidence samples and witness statements.
Some 32 victims were brought to Turkey, where three later died in hospital and underwent examination.
Turkey has said results from those post-mortems show that chemical weapons, possibly sarin, were used.
The attack sparked global outrage, with German chancellor Angela Merkel calling it "barbaric" and saying indications suggest President Assad was behind it.
The Syrian government has denied ever using chemical weapons against "our people" or "terrorists".
Syrian Foreign Minister Walid al Mouallem said the army bombed an arms depot belonging to al Qaeda affiliate, the al Nusra Front, now known as the Fateh al Sham Front, echoing an earlier claim by the Russian defence ministry.
He told a news conference that Islamic State had also been storing chemical weapons from Iraq and Turkey.
Witnesses described seeing victims of the attack choking, fainting and foaming at the mouth.
Donald Trump has described the attack as an "affront to humanity" which "crossed many, many lines" and had changed his attitude on dealing with the conflict, but he stopped short of saying how he would tackle the crisis.
In an interview with The New York Times, he also said Moscow's role in the long-running civil war was "disappointing" - adding it was a "very sad day for Russia because they're aligned".