The US today banned its diplomats from having any contact with the Hamas-led cabinet as it was sworn in by the Palestinian president, Mahmoud Abbas.
The directive, issued to US officials in the region by email, bars them from communicating with Hamas-appointed government ministers, whether they belong to the militant Islamic group or not, US officials told Reuters.
The order took effect in Ramallah at 6pm (1600 GMT), when Hamas formally took power with the swearing-in of its 24-member cabinet.
The first to be sworn in was the prime minister, Ismail Haniyeh.
The ceremony came the day after a general election in Israel that looks set to bring a Kadima-led coalition to power.
The party, founded at the end of last year by Ariel Sharon, has vowed to unilaterally withdraw from parts of the West Bank if an agreement cannot be reached with the Palestinians.
After the win, the Kadima leader, Ehud Olmert, reiterated his intention to proceed with that plan. Israeli officials have ruled out new talks unless Hamas changes its ways.
US diplomats would still be allowed to contact Mr Abbas, his personal office and non-Hamas members of the Palestinian parliament, but America is trying to either sideline Hamas or force it to recognise Israel, renounce violence and abide by peace accords.
The group, which won Palestinian elections in January, is considered a terrorist organisation by the US.
The Hamas MP Mushir Masri today said the group would not abandon its armed struggle if Mr Olmert pursued his plan to unilaterally draw the Israeli borders with the West Bank.
He accused the Kadima leader of trying to gain international approval for his one-sided moves by presenting his plan as a fallback to failed negotiations.
"I think proposing negotiations along with the unilateral plan is only to make the plan pass and market it to the world," Mr Masri told the Associated Press.
Mr Haniyeh said yesterday that unilateral moves by Israel "definitely won't be accepted by the Palestinian people or the Palestinian government".