The US is likely to be in breach of the UN security council's arms embargo on Libya if it sends weapons to the rebels, experts in international law have warned.

After Hillary Clinton said it would be legal to send arms to support the uprising, lawyers analysing the terms of the UN's 26 February arms embargo said it would require a change in the terms for it not to breach international law.

"The embargo appears to cover everybody in the conflict which means you can't supply arms to rebels," said Philippe Sands QC, professor of international law at University College London.

His view was backed by other experts in international law who said they could not see how the US could legally justify sending arms into Libya under the current resolutions.

Clinton told a press conference in London on Tuesday that this month's UN security council resolution creating a no-fly zone and allowing strikes to protect civilians effectively amended or overrode the absolute prohibition on arms to anyone in Libya, "so that there could be a legitimate transfer of arms if a country should choose to do that".

Asked whether the US itself would arm Libya revolutionaries, Susan Rice, the US ambassador to the UN, said: "We have not made that decision but we've not certainly ruled that out."

February's UN security council resolution 1970 on the arms embargo states that all member states must prevent the supply to the Libyan Arab Jamahiriya – the Libyan nation – of arms including weapons and ammunition, military vehicles and equipment, paramilitary equipment and spare parts. The embargo also relates to the provision of technical assistance, training or financial and bans the provision of mercenaries.

It includes an exemption for "other sales or supply of arms and related material, or provision of assistance or personnel, as approved in advance by the committee". The committee was established to oversee the implementation of the embargo and is chaired by José Filipe Moraes Cabral, Portugal's ambassador to the UN.

Professor Nicholas Grief, director of legal studies at the University of Kent, said that to him the 17 March resolution in fact appeared to strengthen the arms embargo by calling for its "strict implementation" by member states.

"I don't see how they can say that reading them together means they can circumvent the arms embargo," he said. "The resolution makes clear it is for the security council to decide whether to strengthen, suspend or lift the arms embargo, not for member states to act unilaterally."

On Monday, the Nato secretary general, Anders Fogh Rasumussen, stressed the importance of respecting the arms embargo. "The UN mandate authorises the enforcement of an arms embargo," he said. "We are not in Libya to arm people but to protect people."

A leading expert on UN law who has advised the British government and asked not to be named said: "The attempt to take the two resolutions together to justify arming the rebels looks like an imaginative interpretation by the US. I don't think the security council had the rebels in mind when it passed the resolution. I would be interested to see what the US argument is in detail."

"The idea of the arms embargo resolution is to limit the supply of arms to both sides, as similar UN embargoes covering Iraq and Haiti have done."

A senior state department official confirmed the US government believed that combined, the 26 February arms embargo and the 17 March security council resolution "give us the flexibility necessary should that decision be taken [to arm the rebellion]".

"Taken together the two resolutions don't preclude the provision of arms to the rebels," the official said.