WASHINGTON — The acting director of the Immigration and Customs Enforcement agency said on Wednesday that he would follow through with plans to send agents into communities to round up and deport undocumented families, in the Trump administration’s latest attempt to deter large-scale migration of Central Americans to the southwest border.

The acting director, Mark Morgan, who has signaled for weeks that there would be a heightened focus on deporting families, told reporters that agents would target more than 2,000 immigrant family members who already have deportation orders.

“Do not come,” Mr. Morgan said in describing the message he wants to send to people from Honduras, Guatemala and El Salvador who think they will be able to remain in the United States once they get across the border. “Do not risk it. Do not pay the cartels an exorbitant amount of money because once you receive due process and get a final order, you will be removed.”

Mr. Morgan’s comments came after President Trump tweeted on Monday that the immigration agency would deport millions of people next week. The president’s tweet alarmed immigrant communities and blindsided immigration agents across the country who described such a massive operation as logistically impossible.