Hillary Clinton, the US secretary of state, has reiterated the US position that it will not deal with or fund a Palestinian government that includes Hamas until certain conditions are met.
Clinton told the House Foreign Affairs Committee on Wednesday that Hamas must renounce violence, recognise Israel and agree to "previous obligations" of the Palestinian Authority.
She said it appeared that Hamas had "no intention" that this would happen, but said the US wanted to "leave open the door".
But Osama Hamdan, a senior member of Hamas in Damascus, said the US was working against the Palestinian people by adopting such conditions.
"Hillary Clinton must understand that there is a Palestinian democracy and there [were] Palestinian elections and someone won those elections," he said.
"She must talk to those people or at least respect the choice of the Palestinians. By her position she is against the Palestinian people [and] she is against [their] choices."
Clinton also did not rule out the possibility of further sanctions against Iran should diplomacy fail over its nuclear programme.
In her first congressional testimony since her confirmation hearing in January, Clinton said the US was confident it could, with the help of global partners, put together a comprehensive sanctions regime against Iran "should we need it".
"We actually believe that by following the diplomatic path we are on, we gain credibility and influence with a number of nations who would have to participate in order to make the sanctions regime as tight and as crippling as we would want it to be," she said.
"We are deploying new approaches to the threat posed by Iran, and we're doing so with our eyes wide open and with no illusions."
Iran has rejected Western allegations that its nuclear programme is intended to develop weapons, saying it is solely for peaceful energy purposes.
Clinton also had heavy criticism for the Pakistani government, saying it was "basically abdicating to the Taliban" in agreeing to the imposition of sharia law in parts of the country.
On North Korea, she said that the US wants to resume six-nation nuclear talks with the isolated nation but the world must not "give in" to the North's "unpredictable behaviour".
And on Sri Lanka, Clinton said the US had been pressing the government to halt the fighting in order to assist civilians and criticised the Tamil Tiger leadership for "little openness" ending their operations.
Some Republican members of the committee pressed Clinton on the decision by the administration of Barack Obama, the US president, to release formerly classified documents on detainee interrogation methods used during the Bush administration.
However, Clinton deflected those inquiries, saying it was not a matter for her to discuss in public.