The US is considering a request by Ukraine for long-range Tomahawk missiles, US Vice-President JD Vance has said.
However, Vance added President Donald Trump would be making the final determination on the matter.
Kyiv has long been calling for its Western partners to provide it with weapons that could hit major Russian cities far from the front line, arguing that they would help Ukraine seriously weaken Russia's military industry and bring the war to an end.
If the cost of continuing the war for Moscow is too high, it will be forced to start peace talks, deputy defence minister Ivan Havryliuk told the BBC.
Kremlin spokesman Dmitry Peskov played down Vance's suggestion, saying there was no panacea that can change the situation on the front for the Kyiv regime.
Tomahawk missiles have a range of 2,500 km (1,550 miles), which would put Moscow within reach for Ukraine.
While Vance remained ambivalent about Ukraine's request for Tomahawks in his remarks on Sunday, the US special envoy to Ukraine, Keith Kellogg, seemed to suggest Trump had already authorised strikes deep into Russian territory.
Asked on Fox News whether Washington had allowed Kyiv to carry out long-range strikes within Russia in specific instances, Kellogg said: The answer is yes, use the ability to hit deep, there are no such things as sanctuaries.
Vance and Kellogg's comments match the US administration's recent change of tone in regard to the war.
Trump is known to have been irritated by Russian President Vladimir Putin's surface willingness to discuss ending the war versus the reality of Moscow's persistent bombardments of Ukraine's cities.
On Sunday, a massive 12-hour strike involving hundreds of drones and nearly 50 missiles left four people dead in Kyiv and at least 70 injured.
To protect its skies from ballistic missiles, Kyiv has asked its Western partners for at least 10 units of Patriot surface-to-air defence systems which can detect and intercept oncoming missiles. Ukraine is hoping that better protection of its cities with air defence systems combined with long-range weapons able to hit Russian targets will help bring Moscow to the negotiating table.
