Condoleezza Rice has criticised reported plans by former US president Jimmy Carter to meet a senior Hamas leader in Syria next week.
"I find it hard to understand what is to be gained by having discussions with Hamas about peace when Hamas is in fact the impediment to peace," the US secretary of state said in Washington on Friday.
Carter, who won the Nobel Peace Prize in 2002, could meet Khalid Meshaal, the exiled leader of Hamas, during a trip to the Middle East that begins on Sunday.
Hamas has said the meeting will take place but Carter is yet to confirm it.
The US state department has urged Carter not to violate foreign policy by meeting Hamas’s political leader.
Rice, who has sought Carter’s advice on Middle East negotiations in the past, described Hamas as "terrorist organisation", that has refused "opportunities to come into line with international standards concerning the Middle East".
The US has demanded that Hamas, which controls the Gaza Strip, renounce violence, recognise Israel, and accept previous agreements between Israel and the Palestinians.
Barack Obama, the US Democratic presidential hopeful, said he will not criticise Carter, although he said he would not meet the Palestinian group.
"I’m not going to comment on former president Carter. He’s a private citizen. It’s not my place to discuss who he shouldn’t meet with," Obama said.
Carter has not publicly backed either candidate in the Democratic race but hinted recently that he supports Obama.
On Thursday Hamas officials said that Carter had requested a meeting with Meshaal, the Palestinian group’s political leader in exile in Syria.
"There is an agreement to hold the meeting and arrangements are under way," Ayman Taha told Reuters, adding that the meeting had been fixed for April 18.
The US-based Carter Center did not confirm the meeting or "any specifics" in Carter’s undisclosed itinerary.
But Sean McCormack, the US state department spokesman, said on Thursday the former US leader was "counselled" against meeting any Hamas representatives because it went against US foreign policy of isolating the group.
The Carter Center said the ex-president was leading a study mission as part of his efforts to "support peace, democracy and human rights" in the Middle East.
"This is a study mission and our purpose is not to negotiate but to support and provide momentum for current efforts to secure peace in the Middle East," it said in a statement.
"Our delegation has considerable experience in the region, and we go there with an open mind and heart to listen and learn from all parties."
Israel, which also calls Hamas a terrorist organisation, has expressed concern over the meeting, which would be the first public contact between a US leader and Hamas officials in two years.