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The US Secret Service is investigating how cocaine was found at the White House on Sunday night, with visitor logs and footage combed for clues.

The discovery in the West Wing, which contains the Oval Office and other working areas for presidential aides and staff, led to a brief evacuation.

Secret Service agents found the powder during a routine inspection in an area that is accessible to tour groups.

President Joe Biden and his family were at Camp David in Maryland at the time.

A senior law enforcement official told the ³ÉÈË¿ìÊÖ's US partner CBS News the substance was found in a storage facility routinely used by White House staff and guests to store mobile phones.

The White House complex was closed as a precaution at around 20:45 local time (00:45 GMT) on Sunday after it was discovered.

A preliminary test later confirmed the substance was cocaine.

The Secret Service will lead a full review of how it got into the White House, press secretary Karine Jean-Pierre said on Wednesday.

White House staff are permitted to give tours of some parts of the West Wing to friends and family. Visitors who are not accredited staff must store mobile phones and other personal belongings in cubicles.

"It was in one of the cubbies," a source familiar with the investigation told Reuters.

Speaking at a daily press briefing on Wednesday, Ms Jean-Pierre said that the area where the cocaine was discovered is a "heavily travelled" part of the White House.

"We have confidence that the Secret Service are going to get to the bottom of this," she said.

President Biden was briefed on the matter, Ms Jean-Pierre added. Mr Biden did not answer reporters' questions about the incident on Wednesday.

Arkansas Senator Tom Cotton, a top Republican on the Senate Judiciary Committee, wrote to the Secret Service's director with a list of questions about how such a drug could end up in one of the world's most carefully guarded buildings.

He asked about the White House's security and visitor screening process, and how many times drugs have previously been discovered at the presidential mansion.

Cocaine is a Schedule II drug under the Controlled Substances Act, meaning it has a high potential for abuse, according to the US Drug Enforcement Administration.

The West Wing is a large, multi-level part of the White House that contains the offices of the president of the United States, including the Oval Office and the Situation Room.

It also houses the offices of the vice-president, the White House chief of staff, the press secretary, and hundreds of other staff who have access.