John Kelly, Donald Trump's choice to lead the department of homeland security, has said that 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 [not] 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 US-Mexico border.
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Earlier on Tuesday, Jeff Sessions, Trump's choice for attorney general, promised to stand up to Trump, his close ally and future boss, saying that he would oppose a ban on Muslims entering the country and enforce a law banning waterboarding even though he had 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 that 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 US refugee programme.
Source: News agencies