In two weeks' time, Barack Obama will accept the Nobel peace prize in Oslo for his "extraordinary efforts to strengthen international diplomacy and co-operation between peoples" and his commitment to "disarmament and arms control negotiations".

Yet on Tuesday, as Americans' attentions were turning to the Thanksgiving holidays, a state department spokesman, Ian Kelly, quietly announced that the Obama administration would not sign the international antipersonnel landmine ban. He also said that the Bush-era landmine policy, a regression from Bill Clinton's position, "remains in effect".

"It is painful that President Obama has chosen to reject the mine ban treaty just weeks before he joins the ranks of Nobel peace laureates, including the International Campaign to Ban Landmines," said Steve Goose, arms division director at Human Rights Watch, summing up the disappointment felt by many at Obama's decision.

The announcement comes just days before more than 150 signatory countries of the mine ban treaty meet in Cartegena, Colombia to review progress toward eradicating the threat of landmines in the world's current and former war zones.

Last year, landmines and other similar devices killed or injured more than 5,000 people, over 60% of whom were civilians and 28% children. By failing to take a strong stand against landmines, the US will appear to condone this human tragedy and make it easier for China, Russia, Iran and other non-signatories to the ban to shirk their responsibilities.

Anti-landmine campaigners and liberal activists had hoped Obama would use the landmine and cluster munitions bans to demonstrate a new commitment to multilateralism, humanitarianism and disarmament. During the campaign he had hinted, though not committed himself to, a more progressive stand than Bush had taken.

Instead, Obama's administration has endorsed his predecessor's unilateral repudiation of the treaty. This has outraged the anti-landmine movement, both in the US and globally.

The International Campaign to Ban Landmines, a coalition of hundreds of NGOs, churches and grassroots organisations worldwide, "strongly condemned" the decision; its US counterpart called the announcement "shocking".

"We cannot understand this shameful decision and we definitely cannot understand President Obama's decision to continue with the Bush policy," said Jody Williams, Nobel co-laureate for her role in the landmine ban. "This decision is a slap in the face to landmine survivors, their families and affected communities everywhere."

While the US has not used landmines since 1991, it has stockpiles of some 10m antipersonnel mines and 7.5m anti-vehicular mines, and has used cluster bombs, which leave behind explosive "duds" that act as de facto mines, in Kosovo, Afghanistan and Iraq.

Obama's apparent approval of a hawkish Bush administration policy has also angered his base supporters, who had hoped his election would usher in an era of liberal, multilateral and gentler foreign policy.

When veteran Democratic senator Patrick Leahy of Vermont endorsed Obama's presidential run in 2008, he told reporters it was because we needed a president who could "reintroduce America to the world". However, this week, Leahy did not hold back in his criticism of Obama.

"The United States is the most powerful nation on earth. We don't need these weapons and most of our allies have long ago abandoned them," said Leahy. "It is a lost opportunity for the United States to show leadership instead of joining with China and Russia and impeding progress."

On Wednesday, in the face of this criticism, the Obama administration seemed to backpedal slightly, saying that a policy review on landmine issues was still continuing. Landmine activists have called on the administration to engage and consult with outside experts, Nato allies who are members of the treaty and organisations working to clear landmines.

As a Nobel peace laureate and the leader of the world's most powerful nation, Obama has a duty to live up to his responsibilities to protect civilians in current and former war zones.

Obama's misstep must serve as a wake up call for concerned liberal citizens in the US and around the world. Just because Obama shares our language, and probably our ideals, if he doesn't feel political pressure from the left, his administration will be tempted to avoid a backlash from the right by maintaining hawkish and unilateralist Bush-era policies.