Trump shocked European allies this week by calling Russian President Vladimir Putin without consulting them or Kyiv beforehand and declaring an immediate start to Ukraine peace talks.
Trump administration officials have also made clear in recent days that they expect European allies in NATO to take primary responsibility for the region as the US now has other priorities, such as border security and countering China.
Asked if he could assure the audience that Ukrainians and Europeans would be at the table for talks, General Keith Kellogg told a global security conference in Munich on Saturday: "The answer to that last question (regarding Europeans), just as you framed it, the answer is no."
Ukrainians, however, will "of course" be at the table, he said, adding it would be foolish to suggest otherwise.
This triggered an immediate rebuke from European leaders.
"There's no way in which we can have discussions or negotiations about Ukraine, Ukraine's future or European security structure, without Europeans," Finland's President Alexander Stubb told the same security conference in Munich.
"But this means that Europe needs to get its act together. Europe needs to talk less and do more."
Stubb said the questionnaire the US sent to Europeans "will force Europeans to think".
A European diplomat said the US document included six questions with one specifically for European Union member states.
"The Americans are approaching European capitals and asking how many soldiers they are ready to deploy," one diplomat said.
NATO Secretary General Mark Rutte also urged Europeans to get their act together.
"And to my European friends, I would say, get into the debate, not by complaining that you might, yes or no, be at the table, but by coming up with concrete proposals, ideas, ramp up (defence) spending," he said in Munich.
France is discussing with its allies the possibility of holding an informal meeting among European leaders on Ukraine to discuss these matters, although nothing has been decided at this stage, a French presidency official said on Saturday.
Polish Foreign Minister Radoslaw Sikorski said it would take place on Monday.
Kellogg told the conference that talks aimed at ending the war between Russia and Ukraine could focus on territorial concessions from Russia and targeting Putin's oil revenues.
"Russia is really a petrostate," he said, adding that Western powers needed to do more regarding effectively enforcing sanctions on Russia.
Earlier, Ukrainian President Volodymyr Zelenskiy called for the creation of a European army, saying the continent could no longer be sure of protection from the United States and would only get respect from Washington with a strong military.
In an impassioned speech to the annual Munich Security Conference of global policymakers, Zelenskiy said an address by US Vice President JD Vance the previous day had made clear the relationship between Europe and the United States was changing.
"Let's be honest - now we can't rule out the possibility that America might say no to Europe on issues that threaten it," said Zelenskiy, speaking as the war triggered by Russia's invasion of his country is set to enter its fourth year.
He said a European army - which would include Ukraine - was necessary so that the continent's "future depends only on Europeans - and decisions about Europeans are made in Europe".
European nations cooperate militarily primarily within NATO, but governments have so far rejected various calls for the creation of a single European army over the years, arguing that defence is a matter of national sovereignty.
A senior official from an eastern member state of the European Union responded sceptically to Zelenskiy's proposal for a European army, saying: "There is a European military force called NATO."
Zelenskiy said Kyiv would never accept a deal made behind its back, and predicted Putin would try to have Trump attend Moscow's May 9 World War Two victory anniversary parade "not as a respected leader but as a prop in his own performance".
