Donald Trump has promised to pursue the largest deportation operation in American history as soon as he takes office.

But the Mexican government and other regional allies have been unable to meet with the incoming Trump administration, according to officials in Latin America, leaving them in the dark about the president-elect’s plans to deport millions of illegal immigrants.

The incoming administration rebuffed requests by Mexico for a formal meeting, insisting that detailed discussions will only begin after Mr. Trump is sworn in next Monday, according to a Mexican official and two people familiar with the exchanges who were not authorized to speak publicly.

The Guatemalan and Honduran governments received similar messages, according to officials from those countries.

“This is not the way things usually work,” said Eric L. Olson, a fellow at the Wilson Center’s Latin American program and Mexico Institute. “Usually there are more informal contacts and some level of discussion by now.”

The incoming administration may want to limit confrontation before ramping up pressure by signing a flurry of executive orders on migration, analysts say, leaving governments in the region scrambling to respond. That would likely strengthen Washington’s hand in upcoming negotiations.