The U.S. said Tuesday it proposed alternative dates for a planned NATO ministerial meeting Secretary of State Rex Tillerson will not attend due to a scheduling conflict.

A State Department official said earlier in the day Tillerson would be unable to attend the April 5-6 gathering of NATO foreign ministers in Brussels.

Tillerson will reportedly participate in President Donald Trump's meeting with Chinese President Xi Jinping in Florida on April 6-7.

The State Department did not specify which dates have been proposed to the trans-Atlantic alliance to reschedule the ministerial, but spokesman Mark Toner said the dates are currently under consideration.

"This is not just a decision for NATO headquarters but it also has to be reached, these dates, by consensus by all 28 allies," he told reporters.

Tillerson will meet "a lot of the allies tomorrow, if not all" during a planned anti-Daesh coalition conference in Washington on Wednesday, Toner said.

Toner confirmed all 27 NATO countries will be represented at the meeting, after the State Department on Monday failed to include Croatia on the list of participants.

He called the omission a "late night gaffe".