Oxfam has received 26 new claims of sexual misconduct, allegedly by its staff, since it was revealed the charity's aid workers used prostitutes in Haiti.

Sixteen of the accusations - which include recent and older incidents - related to the British-based charity's work outside the UK, Oxfam Chief Executive Mark Goldring said on Tuesday.

"I'm sorry for the damage Oxfam has done both to the people of Haiti, but also to wider efforts for aid and development, by possibly undermining public support," Goldring told a parliamentary hearing in London.

The UK's parliamentary committee for international development summoned Goldring and other senior Oxfam staff to give evidence on sexual exploitation in the aid sector.

Earlier this month, reports surfaced that Oxfam employees had paid sex workers while on an aid mission in Haiti, following the country's devastating 2010 earthquake.

The charity fired four staff members for gross misconduct and allowed three others to resign following a 2011 internal inquiry into the sex scandal, the downloading of pornography, and bullying and intimidation during the assignment.

Three members of staff implicated in the report physically threatened a witness during the investigation, according to a redacted version of the internal report released on Monday.

Haitian President Jovenel Moise has said the Oxfam scandal is "the visible part of the iceberg" and called for probes into the conduct of the charity and other aid organisations in Haiti since 2010.

"It is not only Oxfam, there are other NGOs in the same situation, but they hide the information internally," Moise told Reuters news agency on Friday.

The European Union and UK government have said they will review their funding of Oxfam in light of the allegations.

Oxfam, which operates in 35 countries worldwide, received 176 million pounds ($243m) of funding from the UK government and other public authorities during the 2016-17 financial year, 43 percent of the charity's 408.6 million pounds ($564m) of total income.