Last week US officials said that the deployment had been scrapped, the latest move by President Donald Trump's administration to slash troop numbers stationed in European NATO allies.

Vance -- one of the administration's most vocal critics of Europe and a strong skeptic about US aid to Ukraine -- said Trump had been urging European allies to take more of the burden for their defense since his first term.

"We have got to have more sovereignty and more of Europe standing on its own two feet. That will continue to be our policy in Europe," Vance told a briefing at the White House.

But when asked about the 4,000 troops and Poland, Vance replied: "It is a delay in troop rotation. Those troops could go elsewhere in Europe. We could decide to send them elsewhere.

"We actually haven't made the final determination about where those troops are ultimately going to go."

A senior US military officer told a congressional hearing last week that the head of US European Command had "received the instructions on the force reduction" in Poland, a key ally on NATO's eastern flank with Russia.

Trump has appeared determined to punish allies who have failed to back the Middle East war or contribute to a peacekeeping force in the crucial Strait of Hormuz waterway, which Iran has effectively closed.

The Pentagon announced at the beginning of May that Washington would pull 5,000 troops from Germany.