The Republican chairman of the powerful US Senate Intelligence committee stepped down from his position Thursday after the FBI seized his cellphone in a probe of alleged insider stock trading tied to the coronavirus pandemic. Senate Majority Leader Mitch McConnell said Richard Burr would be stepping aside temporarily while the FBI investigation is ongoing. "We agreed that this decision would be in the best interests of the committee and will be effective at the end of the day tomorrow," McConnell said in a statement. Burr is under investigation over whether he used his insider access to highly classified intelligence to sell stocks in February -- before the coronavirus pandemic struck, and while Americans were being told the virus's threat was low. The Los Angeles Times said federal agents wielding a warrant seized his cellphone late Wednesday at his Washington home. Earlier they accessed Burr's personal files on his iCloud account, and information from that led them to the phone, the newspaper reported, quoting law enforcement officials. NBC News also reported on the cellphone seizure, citing an unnamed senior law enforcement official. - Dumped stocks, warned donors - One of the most respected and relatively non-partisan Republican senators, the North Carolina lawmaker came under investigation after reports showed he had dumped stocks and warned donors of the looming COVID-19 pandemic in February -- as the White House played down the danger. Burr, who receives almost daily briefings from the US intelligence community on threats to the country, himself wrote on the Fox News website on February 7 that the US government was "better prepared than ever" for the COVID-19 virus, assuring Americans that they were well-protected. But on February 13 the North Carolina senator and his wife suddenly sold off between $628,000 and $1.7 million in stocks, the ProPublica media group revealed in March, citing financial filings. On the same day, Burr's brother-in-law sold as much as $280,000 worth of shares, ProPublica reported last week. Since then stock markets have plunged as the disease swept the world. Nearly 1.4 million Americans have been confirmed infected and over 84,000 died, more than any other country. Burr, who receives much of the same intelligence that the White House does, clearly had a different private view of the threat than the government's public stance. Two weeks after his share sales, Trump assured the public that the 15 US coronavirus cases so far reported could be the peak. The same day Burr told a private gathering of wealthy donors that coronavirus was a threat akin the 1918 Spanish Flu, which killed tens of millions. "There's one thing that I can tell you about this: It is much more aggressive in its transmission than anything that we have seen in recent history," he said.