President Vladimir Putin has informed his US counterpart about Russia's impending fierce response to Ukraine's attacks on strategic air bases.
In the latest security warning on June 4, the US Embassy in Kiev advised Americans not to ignore airstrike warnings and take shelter, warning of "the risk of further intense airstrikes".
US President Donald Trump wrote on the social network Truth Social on June 4, revealing details about the unprecedented phone call with President Vladimir Putin the same day.
"Russian President Vladimir Putin has said very strongly that he will have to respond to recent attacks by Ukraine on airports with Russian strategic bombing aircraft," President Donald Trump wrote.
The US State Department also issued a security warning just a few hours earlier, advising Americans currently in Ukraine to "determine their shelters in advance" and "reserve water, food and medicine".
"Russia has intensified missile and drone attacks on Ukraine in recent weeks and there is still a risk of further significant airstrikes," the announcement said.
On June 1, Ukrainian drones attacked many Russian air bases in a coordinated attack against long-range bombers capable of carrying nuclear weapons.
Moscow said most of the drones were stopped, not confirming any damage. Russia has launched Iskander missiles and hundreds of UAVs at Ukrainian military targets.
Kiev also targeted many Russian civilian sites last weekend, collapsing two railway bridges in Bryansk and Kursk, killing at least seven people and injuring more than 120.
On June 4, President Putin described the rail sabotage in Russia's Bryansk and Kursk regions as "certainly a terrorist act" carried out by "illegal regime in Kiev".
According to foreign policy adviser Yury Ushakov, President Putin informed President Trump that all of these strikes were aimed at skewing direct talks between Russia and Ukraine, in which the second round took place in Istanbul, Turkey on June 2.
The two leaders agreed to continue contacting about Ukraine at both the highest level and through other channels. Trump described the phone call as "a good conversation," although he noted that it was "not a conversation that would lead to immediate peace."
