White House officials are clearly instructed: Do not use your personal phones for official business. But critics allege some aides appear to have continued with this practice anyway, and it is coming under renewed scrutiny alongside questions about the use of personal email accounts.

The inquiries into private communication could prove uncomfortable for President Donald Trump, who relentlessly attacked Democratic opponent Hillary Clinton for her use of a private email account and server during her time as secretary of state.

Many current and former Trump White House officials have used private email accounts and texts from personal phones for private conversations, sometimes using encrypted messaging apps.

That is, despite clear directives not to use personal devices for government business and to keep the records if they do.

House lawmakers have requested more information about the use of private email addresses, texts and messaging apps on personal phones.

They are also asking about the oversight and record-keeping policies of the Trump White House. They acted after information emerged that White House adviser Jared Kushner set up a private email account after the election to conduct official business.

The New York Times also recently disclosed the names of six close Trump advisers, including Kushner, Steve Bannon and Reince Priebus, who have used private email to discuss White House matters. Bannon and Priebus no longer work for the Trump administration. The extent of private communications on personal phones and the keeping of such records is not clear.

Rep. Trey Gowdy, a South Carolina Republican who chairs the House Oversight and Government Reform Committee, and the top Democrat on the panel, Rep. Elijah Cummings have sent letters to the White House general counsel and the State Department. They have requested for more details on whether staffers are using personal emails, texting or encrypted messaging applications, and want to know if they are preserving the records.

The Presidential Records Act requires senior White House staff to keep an account of their professional communications, with the records eventually transferred to the National Archives. Electronic communications outside official channels, such as private email or text messages on a staffer's personal phone, are supposed to be copied to a government account within 20 days.

White House aides are instructed as part of their induction not to use personal devices for official business and are told to keep records if they do, according to two people with knowledge of administration practices.

A memorandum went out to all White House personnel in February outlining the rules. The memo, provided to The Associated Press, states that record-keeping rules also applied to "other forms of electronic communication, including text messages".

The memo also stipulated: "You should not use instant messaging systems, social networks, or other internet-based means of electronic communication to conduct official business without the approval of the Office of the White House Counsel."

"Legally, the case is clear - you're supposed to save this stuff," said Alex Howard, deputy director of the Sunlight Foundation, which advocates for transparency and open record-keeping in government.

Howard said that White House officials who sent and received messages via private channels did not necessarily violate the law - if they later forwarded those off-the-books communications to an official government account or preserved them in some other fashion.

"People will make mistakes," he said. "The key is, are those mistakes intentional."

'We get instructed on this one pretty regularly'

One reason White House aides text from private phones is simple. They cannot send texts from their official phones, a policy rule during the Obama administration. When Blackberry devices were standard, a White House communications system automatically archived those messages.

When smartphones supplanted Blackberries, however, White House information technology administrators adopted a new policy: No texts at all.

"With iOS and text, you could get messages (and malware) from anyone," said Tony Scott, Barack Obama's federal chief information officer from 2015 until the end of Obama's second term. He said the decision to disable texting was made "more from a security perspective than anything else".

Trump White House officials are not the first to come under scrutiny over private communications. In 2010, the White House deputy chief technology officer, Andrew McLaughlin, was reprimanded for using a Gmail account to communicate with his former colleagues at Google.

White House spokeswoman Sarah Huckabee Sanders told reporters that the use of private email accounts by staff is "to my knowledge, very limited".

"White House counsel has instructed all White House staff to use their government email for official business, and only use that email," she said, adding that "we get instructed on this one pretty regularly".

Kushner's lawyer, Abbe Lowell confirmed Kushner's use of a personal email in his first few months of joining the administration. He said the emails usually involved news articles and political commentary. Lowell also said any non-personal emails were forwarded to Kushner's official account and "all have been preserved in any event".

There are considerable differences between Clinton's email practices and what is known about the Trump administration so far.

Clinton maintained multiple private servers, and an FBI investigation found tens of thousands of emails, including many with classified material. While some Trump officials used private accounts, there is no evidence so far that classified material was transmitted through private email accounts.