WASHINGTON — At least 19 Immigration and Customs Enforcement investigators are seeking to dissolve the agency, concerned that the Trump administration’s crackdown on illegal migrants has limited their ability to pursue national security threats, child pornography and transnational crime.

In a letter sent last week to Kirstjen Nielsen, the homeland security secretary, the special agents proposed creating a stand-alone investigations unit and another agency to handle immigration detention and deportation. The request was sent as a growing number of Democrats and immigration-rights advocates have called for eliminating ICE.

Investigations “have been perceived as targeting undocumented aliens, instead of the transnational criminal organizations that facilitate cross border crimes impacting our communities and national security,” wrote the agents from Homeland Security Investigations, which is a branch of ICE. The Texas Observer first reported the letter.