"The United States does not support political parties that want to destroy our ally Israel," George Bush, the US president, said on Thursday. "People must renounce that part of their platform."
That Hamas had won so overwhelmingly and fairly - Jimmy Carter, the former US president, said the elections in the West Bank and Gaza Strip were "completely honest" - only compounded the dilemma for foreign governments.
They both hailed the smooth vote, and expressed dismay at Hamas' taking nearly two-thirds of the 132 parliament seats.
The resistance group has carried out dozens of suicide bombings, seeks Israel's destruction and has said that it opposes peace talks and will not disarm.
"We must respect the election result, although it was not the outcome we had wished," Anders Fogh Rasmussen, Denmark's prime minister, said.
Concern in Europe
In France, Dominique de Villepin, the prime minister, said renouncing violence, accepting progress towards peace, and recognising Israel and existing peace accords were "indispensable" conditions for working with "a Palestinian government of any kind".
"Hamas won," said Elie Wiesel, the Nobel Peace Prize winner. "Hamas is surely not a democratic movement. Its ideas are surely not humanistic ideas.
"What do we do now?"
There were calls from the Arab and Islamic worlds for Western governments to accept the result.
Hamas says it opposes dialogue
with Israel and it will not disarm
"One has to adjust to ground realities," said General Pervez Musharraf, the Pakistan president.
European governments and the US planned meetings to co-ordinate their response. Condoleezza Rice, the US secretary of state, was due to meet Monday in London with UN, Russian and European officials.
"You cannot have one foot in politics and another in terror," Rice said, adding that for the US, Hamas was still a terrorist organisation.
'Very bad result'
Concern crossed political divides, with traditional supporters of the Palestinian cause - such as Italy's centre-left opposition - among those expressing worry.
The Italian government said Hamas' victory could indefinitely postpone any chance of Israeli-Palestinian peace and make the creation of a Palestinian state more difficult.
"It is a very, very, very bad result," Silvio Berlusconi, the prime minister, said.
European Union foreign ministers who meet Monday will discuss what to do, and German leader Angela Merkel will visit Mahmoud Abbas, the Palestinian president, and Israeli leaders.
Hamas is being urged to drop its
stated goal to destroy Israel
Austria, which holds the EU's rotating presidency, issued a
statement on behalf of the 25-nation bloc stating "there is no place in a political process for groups or individuals who advocate violence".
"Of course, we recognise the mandate for Hamas because the people have spoken," Tony Blair, the British prime minister, said.
"But I think it is also important for Hamas to understand that there comes a point, and that point is now following that strong showing, where they have to decide between a path of democracy or a path of violence."
Aid at stake
The EU has given millions of euros in aid to the Palestinian Authority to help reconstruction efforts in the Gaza Strip and the West Bank - funding that was called into question following Hamas' win.
A senior European Parliament lawmaker, Elmar Brok, warned of a possible cut-off of aid if Hamas did not change its policies.
"It is obvious that the EU would never countenance funding a regime that continued an armed fight against Israel," said Ignasi Guardans, a Spanish member of the parliament.
"But we cannot push for democracy and then deny the result of free and fair elections."