Rupert Murdoch has moved to quell growing disquiet at Britain's top-selling newspaper and lifted the suspensions of all arrested staff.

In a memo to employees, the media mogul confirmed he will begin publishing The Sun seven days a week by launching a new paper called The Sun on Sunday "very soon".

While pledging "unwavering support" for his journalists, he also vowed to root out wrongdoing at News International. The tabloid has been rocked by the arrests of 10 current and former senior reporters and executives since November over alleged corrupt payments to public officials.

Some Sun journalists have voiced anger that News Corporation's Management Standards Committee (MSC) - formed to clean up the company following the phone-hacking scandal - gave police the information that led to the arrests.

On Friday the spotlight fell on the News Corporation chief executive after he flew into the country in his private jet to take charge of the most recent crisis at his stable of newspapers.

He arrived at The Sun headquarters, in Wapping, east London, to reassure staff this morning and is understood to have spent the afternoon on the newsroom floor, accompanied by his eldest son Lachlan.

A source played down the significance of the absence of Mr Murdoch's younger son James, chairman of News International. "James Murdoch has other commitments and is out of the country, and asked Lachlan to accompany his father," he said.

In the memo, received by staff on Friday afternoon, Mr Murdoch said the recent arrests - including nine in the past three weeks, among them The Sun's deputy editor, picture editor and chief reporter, were "a source of great pain" for him.

While he said illegal activities "simply cannot and will not be tolerated," he insisted that journalists' "legitimate" confidential sources would be protected. Paying tribute to his staff's "exceptional journalism", he set out a vision to make The Sun an "example to Fleet Street of ethical journalism".

Away from News International, Mr Murdoch's announcement caused some consternation. Labour MP Chris Bryant, who has led the phone-hacking campaign, said the decision to launch the new Sunday tabloid was "massively premature".