The FBI has searched a mail facility near Miami, as investigators try to find who is behind a series of suspected explosive packages.
Devices have been sent to eight high-profile people, including ex-President Barack Obama and actor Robert De Niro.
Unnamed officials told US media that investigators believe at least one was sent from Florida.
The FBI have not released any details of their investigation.
Similar packages have also been sent to former Vice President Joe Biden and former Secretary of State Hillary Clinton, among others.
The postal facility searched is in Opa-locka, where security footage was being scrutinised. A bomb squad and canine unit accompanied federal officials, Miami-Dade County Police said.
On Thursday evening, the Time Warner Center in New York was evacuated after reports of a suspicious package, but it was later declared a false alarm. The building is home to news network CNN, which received one of the devices by post the previous day.
Earlier, FBI Assistant Director William Sweeney confirmed that the white powder found in the package sent to CNN “did not present a biological threat”.
Mr. Sweeney said thorough examinations of all the packages were under way at the FBI laboratory in Quantico, Virginia, outside Washington DC.
New York Police Commissioner James O’Neill could not confirm whether all the devices were intended to explode, but he said officials “are treating them as suspected explosive devices”.
“This has to be taken with the utmost seriousness,” he said. “As far as a hoax device? We’re not treating it that way.”
Mr. O’Neill added that authorities “do not know at this time” whether there were additional devices in the mail. He said police were working with postal service officials “to make sure if there are any out there, we identify them quickly”.
On Thursday morning, the FBI said Mr. Biden received two suspect packages and a similar package was found at a New York restaurant owned by Mr. De Niro.
A suspected explosive device was found at a building in Manhattan early on Thursday, local time. It is home to Mr. De Niro’s production company and the Tribeca Grill restaurant.
New York City Mayor Bill de Blasio praised the “really quick-witted work of a security guard” who alerted authorities.
According to the Associated Press, the security guard was off work on Thursday and had seen an image in a news report of the packages others had received.
That individual then recalled spotting something similar in the building’s mailroom and immediately called authorities who removed the device around 06:30 (10:30 GMT), AP reports.
CNN’s New York office was evacuated on Wednesday morning, after the package addressed to Mr Brennan was found in its mailroom.
Singapore trader denies laundering millions for North Korea
A Singaporean trader wanted by the FBI for allegedly helping North Korean entities evade US sanctions has flatly denied “all charges” against him.
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Tan Wee Beng told the BBC that he had only learned of criminal charges against him via news reports.
“Nobody has contacted me. The FBI has not called me, the Singapore police have not called me,” he said.
US Federal Prosecutor Geoffrey Barman on Thursday called Mr. Tan “a fugitive from American justice”.
In the same justice department statement, FBI Assistant Director William Sweeney said the Singaporean “conducted illicit transactions totalling millions of dollars in support of North Korean entities in blatant violation of a host of economic sanctions the United States has established against North Korea and North Korean entities”.
The US Treasury has now placed sanctions on Mr. Tan and two companies he is connected to – Wee Tiong (S) Pte Ltd and WT Marine Pte Ltd.He is a director of Wee Tiong (S) and the managing director of WT Marine.
Mr. Tan, a high-profile businessman, has over several years “fulfilled millions of dollars in commodities contracts for North Korea”, the treasury department said.
An US federal arrest warrant was issued for Mr. Tan on 29 August but the Department of Justice announced its indictment against him on Thursday.
He has been charged with conspiring to violate US sanctions, as well as bank fraud and money laundering.
“I found out only today through the internet. It came as a shock to me,” the 41-year-old told the BBC in a phone call on Friday morning in Singapore. He said he denied all the accusations.
“We are an international trading company, and not a front [for laundering],” he said, adding that he had instructed lawyers to defend him.
Mr. Tan also disputed claims by the FBI that he was “at large”. A request for comment has been sent to Singapore police.
The US and Singapore have an extradition treaty but it only covers specific offences and does not include money laundering.
Mr. Tan was once seen as a leading young Singaporean entrepreneur having been named an entrepreneur of the year in 2011 by leading accounting firm EY.
Under his stewardship, annual revenue at Wee Tiong increased by 131 percent in a decade to more than $460 million Singapore dollars ($330m), the Straits Times reported in 2015.
