The step comes a day after Iran pledged $50 million to help fund the Palestinian Authority.
Sean McCormack, the US State Department spokesman, said: "We'd seek a little clarity from the government of Qatar as to exactly what their intentions are, to whom they actually intend to give this money and under what circumstances."
The Gulf Arab state said the decision "stems from Qatar's support for the Palestinian people".
A foreign ministry official told Qatar's state news agency that part of the money was the country's contribution to the $55 million a month pledged by Arab leaders to Hamas at a March summit in the Sudanese capital, Khartoum.
The Palestinian government faces serious financial shortfalls after Israel, the European Union and the United States all withheld funding after Hamas's victory in polls earlier this year.
They demanded Hamas renounce armed resistance, recognise Israel and abide by existing deals.
Iran announced on Sunday that it was to give $50 million in aid to the Palestinians after a conference in Tehran attended by Khalid Mishaal, a Hamas leader.
Mishaal said that Hamas had inherited an empty treasury and had $1.7 billion in debts after its election win in January.