The public disagreement may be uncomfortable for Mr Kushner as Saudi Arabia, a close ally of the Trump administration, was one of the only Arab states to fully support the Bahrain summit.
While several other countries, including Jordan and Egypt, sent junior ministers to the conference, Saudi Arabia boosted Mr Kushner by sending both its finance minister and the head of its public investment fund.
Some Palestinians have questioned whether Saudi Arabia will stick to its support for a Palestinian state, but for now Riyadh appears willing to publicly contradict the US.
Neither the Israeli nor Palestinian governments are attending the conference and the Palestinians have accused Mr Kushner of trying to use the lure of financial rewards to get them to surrender their political goals.
Speaking in front of an audience that included Tony Blair and Christine Lagarde, the head of the International Monetary Fund, Mr Kushner laid out details of his $50 billion economic investment plan for Gaza and the occupied West Bank.