The number of serious incidents of sexual harassment, bullying and abuse reported to the Charity Commission in the three months following the Oxfam sexual abuse scandal has risen to more than 1,150.

The total number of serious incidents reported by charities from February to May this year reached the same level as during the whole of 2016/17.

The commission said that out of the 1,150 reports received since February, 734 new cases have been opened relating to safeguarding concerns. The reports varied in severity, said the watchdog, with some relating to risks as well as actual incidents of harm identified by organisations.

A significant number of the allegations reported to the charity watchdog came from the group of 179 charities contacted by Penny Mordaunt, Britain’s international development secretary. Mordaunt sought urgent assurances that all incidents of potential abuse had been reported to the commission after revelations of misconduct involving Oxfam staff began to emerge.

The commission refused to identify the charities involved as they were still under investigation.

In February, a temporary safeguarding taskforce was set up to handle the increasing number of reports by domestic and international charities.

A review of historic reports of serious safeguarding incidents was also opened by the commission, which says it has now investigated 95% of the 5,500 reports dating back to 2014. Of these incidents, 3,000 involved allegations of potential criminal behaviour.

Aside from one case that has now been reported to the relevant authorities, the commission said it has not yet found any that warrant serious or urgent concern.

On Tuesday, during an evidence session on sexual abuse and exploitation in the aid sector, Helen Stephenson, the commission’s chief executive, told an international development committee, that although the number of serious reports were still rising, the pace had levelled off.

She said that as the vast majority of the 17,000 charities registered by the commission were very small, it was crucial all organisations were supported and encouraged to be accountable and transparent when dealing with abuse allegations.

Mordaunt told the committee she was confident that, because of actions taken since February, predatory individuals had “moved out of the sector”.

“The message from us is that we have made good strides and other donors are coming with us and if you are a predatory individual then the time to move on is now,” she said.