John Kelly, Donald Trump's pick to lead the department of homeland security, has said tightening the country's border will be his top priority in his new role.
Speaking before a Senate confirmation hearing on Tuesday, Kelly called for a "layered defence" on the southern border that would include the possible use of drones and sensors.
"A physical barrier in and of itself will not do the job," Kelly told a Senate Homeland Security and Governmental Affairs Committee hearing.
A layered defence, he said, would include better partnerships with some Latin American countries as far south as Peru and border patrol agents, as well as technology such as drones that would work in "places that perhaps the wall can't be built or will be built any time soon".
He said such tactics were needed because Trump's plan to build a wall along the border to stop undocumented immigrants would not be sufficient.
Deportations reached record levels under President Barack Obama, whose administration deported more than 2.5 million people between 2009 and 2015.
A large wall already exists on much of the United States-Mexico border.
Earlier on Tuesday, Jeff Sessions, Trump's pick for attorney general, promised to stand up to Trump, his close ally and future boss, saying he would oppose a ban on Muslims entering the country and enforce a law against waterboarding even though he voted against the measure.
Civil-liberties advocates seized on Sessions' voting record and his appearances before groups that espouse anti-Muslim and anti-immigrant views.
Sessions said he would not support banning anyone from the United States on the basis of religion and that Trump's intentions were to restrict people from countries harbouring "terrorists", not all Muslims. Elected on November 8, Trump at one point campaigned on a proposal to temporarily ban Muslims from entering the country.
Sessions said he favoured "higher intensity of vetting" for refugees seeking to enter the country but that he would oppose ending the United States refugee programme.
Aljazeera