The UK’s Saudi Arabian embassy told the BBC the allegations were “categorically false”.
Responding to a parliamentary question on Tuesday, Theresa May said ministers were “considering advice on what is able to be published and will report to Parliament with an update in due course”.
The report, which has been in Ms May’s personal possession for six months, was first commissioned by David Cameron in 2015 following an agreement with the Liberal Democrats to get their support for Syrian air strikes.
Since coming to power in July last year, Ms May has courted the conservative kingdom, which is one of the main buyers of UK-made arms.
Earlier this year, the Government approved £3.5bn-worth of arms exports licences to the Gulf state.
Several British ministers have visited Saudi Arabia over the last year to cultivate trading relationships as the UK looks for post-Brexit trading partners and the kingdom, under new Crown Prince Mohammad Bin Salman, is trying to diversify its economy away from oil.