New York  - The new US administration under President Barack Obama pledged Monday to work with the United Nations, which newly appointed US Ambassador Susan Rice described as a "vitally important institution" with great potential.

Rice presented her credentials to UN Secretary General Ban Ki-moon at UN headquarters in New York on her first day at work and spent 45 minutes in discussions with Ban on a range of topics from climate change to the crisis in the Middle East.

While praising the UN potential, Rice said that "it still has room for improvement."

"We touched on the challenge about how to make this organization efficient and effective, and pursue the process of reform to make it more suitable to the challenges in the 21st century," Rice told reporters.

Rice replaced Zalmay Khalilzad, an Afghan-born US diplomat who was restrained by former president George W Bush's lukewarm commitment to fighting climate change and adherence to international justice as promoted by the International Criminal Court at The Hague.

Rice cited a few crises that the Obama White House would have to deal with as a priorities in coming months - "the Middle East and Iran's nuclear issues."

On Iran, she said she will work closely with the other four permanent members of the UN Security Council - Russia, China, France and Britain - and Germany to engage constructively with the Tehran government to end its nuclear programme suspected of manufacturing nuclear weapons.

"We will look to maintain pressure on ending Iran's nuclear programe," she said. "Dialogue and diplomacy will go hand in hand. Iran needs to meet its obligations defined by UN Security Council resolutions and its refusal to do so will only cause pressure to increase."

On the situation in the Gaza Strip, Rice reiterated the position adopted by the UN and US that the ceasefire between Hamas and Israel must be durable and lasting and that humanitarian relief to Gaza residents must be more effective. dpa