A four-star US Air Force general has warned of a conflict with China as early as 2025 –- most likely over Taiwan –- and urged his commanders to push their units to achieve maximum operational battle readiness this year.

In an internal memorandum that first emerged on social media on Friday, and was later confirmed as genuine by the Pentagon, the head of the Air Mobility Command, General Mike Minihan, said the main goal should be to deter "and, if required, defeat" China.

"I hope I am wrong. My gut tells me we will fight in 2025," Minihan said.

Laying out his reasoning, Minihan said Taiwan's presidential elections next year would offer Chinese President Xi Jinping an excuse for military aggression, while the United States would be distracted by its own contest for the White House.

"Xi's team, reason, and opportunity are all aligned for 2025," he added.

The memorandum also calls on all Mobile Command personnel to go to the firing range, "fire a clip" into a target and "aim for the head."

A Pentagon spokesperson responded to an AFP email query about the memo saying, "Yes, it's factual that he sent that out."

Senior US officials have said in recent months that China appears to be speeding up its timeframe to seize control of Taiwan, a self-governing democracy claimed by Beijing.

China staged major military exercises in August last year, seen as a trial run for an invasion after a defiant visit of solidarity to Taipei by then House Speaker Nancy Pelosi, who at the time was second in line to the White House.

The United States switched recognition from Taipei to Beijing in 1979 but sells weapons to Taiwan for its self-defense.

A growing number of US lawmakers have called for ramping up assistance, including sending direct military aid to Taiwan, saying that Russia's invasion of Ukraine underscores the need for early preparation.