The U.S. Secret Service sent letters to congressional leaders on Monday seeking to activate 24-hour protection for Republican presidential candidates Donald Trump and Ben Carson, Fox News reported on Monday.

Leaders of Congress have to sign off on the proposal, which would activate a rotation of 260 agents for the two candidates, the cable television channel reported, citing unidentified sources.

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Carson's campaign requested protection from the Secret Service after the number of threats made against him increased, Fox reported. Carson's campaign told Reuters it would not comment on campaign security issues. 

Trump has also sought Secret Service protection as his campaign rallies have grown. Fox News reported his campaign made contact with the Secret Service on Friday.

The request is likely to be approved this week, Fox said.