Washington, Feb 21 (IANS): The White House notified the Kremlin of Joe Bidens intention to visit Kiev hours before he departed for Ukraine, it has been revealed, as the details began to emerge of how the US President pulled off his high-profile diplomatic coup.

Meticulously planned over several months by a tight circle of key advisers, Biden's visit was described as "unprecedented in modern times" by his National Security Adviser (NSA) Jake Sullivan, on the grounds that it was the first time a US President had visited "the capital of the country at war where the United States military does not control the critical infrastructure", the Guardian reported.

"We did notify the Russians that President Biden will be travelling to Kiev," Sullivan said.

"We did so some hours before his departure for deconfliction purposes, and because of the sensitive nature of those communications I won't get into how they responded or what the precise nature of our message was, but I can confirm that we provided that notice," the Guardian quoted the NSA as saying.

The US informed Moscow to avoid any misunderstanding or misjudgment between the two nuclear-armed powers, according to accounts from Washington.

Biden crossed into Ukraine at about 10 p.m. on Sunday night, having quietly boarded a train in the Polish town of Przemysl.

His motorcade pulled up alongside his carriage allowing him to board unseen.

His security detail took up most of the train's eight carriages.

The journalist and photographer accompanying the President were sworn to secrecy and notified of the rendezvous arrangements under the title: "Arrival instructions for the golf tourney."

Prior to departure they had to hand over their phones, which were not returned until arrival in Kiev, the Guardian reported.