The weekend talks come as President Vladimir Putin, in an annual news conference, vowed to press ahead with his military offensive in Ukraine, hailing battlefield gains nearly four years into his war.
President Donald Trump’s envoys have pressed a plan in which the US would offer security guarantees to Ukraine, but Kyiv will likely be expected to surrender some territory, a prospect resented by many Ukrainians.
But Rubio said that ultimately both sides had to agree to a deal.
“There’s no peace deal unless Ukraine agrees to it,” Rubio told a news conference in Washington.
“This whole narrative that we’re trying to force something on Ukraine is silly,” Rubio said.
“We can’t force Ukraine to make a deal. We can’t force Russia to make a deal. They have to want to make a deal.”
Rubio said he may join talks in Miami, his hometown, on Saturday.
Trump’s global envoy Steve Witkoff and son-in-law Jared Kushner are leading the talks, which will include top Ukrainian negotiator Rustem Umerov as well as top officials from Britain, France and Germany.
Russian officials – reportedly including Kremlin negotiator Kirill Dmitriev – and US officials are expected to meet separately in Florida over the weekend.
Umerov said on social media that he and Andriy Gnatov, the chief of staff of the Ukrainian armed forces, will report back to President Volodymyr Zelensky after the Miami talks.
“We are committed to a constructive process,” Umerov wrote.
“We are acting clearly in line with the priorities defined by the president: Ukraine’s security must be guaranteed reliably and in the long term.”
The talks are part of a flurry of winter diplomacy in sunny Miami. Witkoff and Kushner are also holding talks on the Gaza ceasefire with officials from Egypt, Qatar and Turkey.
Trump has made ending the Ukraine and Gaza wars the centrepiece of his second-term effort to be a self-proclaimed “president of peace”.
But resolving the situation in Ukraine has, by his own admission, proved far harder than he expected.
Putin vows to press on
Russian attacks on Ukraine have not ceased during talks, with a deadly ballistic missile strike on Ukraine’s strategic Black Sea coast on Friday.
“The enemy struck the port infrastructure of the Odesa region – seven dead, fifteen wounded,” Odesa regional governor Oleg Kiper said on social media.
Witkoff and Kushner met Umerov in Miami earlier this month without European involvement and travelled to Moscow to hold talks with Putin.
In November, the US shocked Europe by unveiling a 28-point plan to settle the war that overlooked the continent’s main powers and was widely seen as favouring Russia.
The plan was amended by Ukraine and Europe, but Russia had yet to react to it, with Putin saying Friday that “the ball is now fully and completely” in the court of Kyiv and its Western allies.
“Our troops are advancing along the entire line of contact,” Putin told his news conference.
“I’m sure that before the end of this year we will still witness new success,” he added.
Russia has been making steady gains in the east of Ukraine after failing to quickly topple the Kyiv government and seize the country in February 2022.
Land remains the key stumbling block in the talks, and a source familiar with the negotiations told AFP earlier this week that the US was pushing Kyiv to cede territory in the eastern Donetsk region.
Kyiv, meanwhile, secured a desperately needed lifeline as EU leaders struck a deal Friday to provide Ukraine a loan of 90 billion euros to plug its looming budget shortfalls.
But the EU failed to agree on using frozen Russian assets to come up with the funds.