Kirstjen Nielsen resigned from the US Secretary of Homeland Security despite Trump's claims for a tougher anti-immigration policy

US President Donald Trump announced Sunday that the Secretary of National Security Kirstjen Nielsen, a front-line advocate of his government's controversial immigration policy, will step down.

"National Security Secretary Kirstjen Nielsen will step down and I want to thank him for his services," the president wrote on his Twitter account. "I am pleased to announce that Kevin McAleenan will be Acting Secretary"he added.

The portfolio manager for Homeland Security and Immigration left the presidential cabinet after Trump publicly and privately claimed greater harshness in the immigration affairs. However, his work in the national security sector has been criticized by human rights defenders in the country.

Nielsen was responsible for launching an aggressive immigration policy championed by Trump and including the separation of families immigrants with minors when they crossed the border illegally with Mexico for months, migratory veto against Muslim-majority countries and the regulations for limit asylum at the Mexican border.

The former servant joined the Trump government in January 2017 as badistant secretary then, John Kelly. When Kelly left for the White House as chief of staff in July 2017, Nielsen looked like her second but two months later, she was back in the Department of Homeland Security, this time as secretary.

In this position, he has become the face of the Trump Administration's anti-immigration policy, including the criticized practice of separating migrant children from their parents. It has long been said that Nielsen's relationship with the president was difficult. But despite reports that the president was constantly complaining about her performance, she remained faithful.

Last month, he defended Trump 's national emergency declaration to secure funds for one of his flagship projects: the wall at the border between the United States and Mexico.

The news of cabinet changes was revealed after the meeting between Nielsen and the tycoon Sunday afternoon at the White House. According to a senior manager of the administration, his resignation is part of a series of reforms designed by Trump's senior advisor, Stephen Miller.