President Joe Biden is reluctant to allow Ukraine to use long-range missiles to attack Russia due to fear of a military escalation before US elections.
France and the UK support Ukraine's use of missiles to balance a potential negotiation with Russia.
Putin suggests that if Ukraine attacks Russia with missiles, the US and other NATO countries will be seen as direct participants in the war against Russia.
Putin has managed to normalize the presence of Russian troops in Ukraine, despite the illegality of the situation.
Ukraine feels a need to expand its victories in order to negotiate on equal terms with the Kremlin.
Neither the US nor Germany appear willing to run the risk of a war escalation sparked by testing Putin's threats.
Ukraine will have to wait for the outcome of the US Presidential Election for a potential shift in its support.
Conclusion: Biden's caution is a risky strategy and difficult to sustain in the long term, but acceding to Ukraine's demands could trigger a chain of unforeseeable events.