As UN helicopters bombarded the arsenal of Laurent Gbagbo, his spokesman condemned what he called "illegal acts" and "war crimes" aimed at assassinating the entrenched ruler of Ivory Coast.
This was expected criticism from a regime under attack. But there have also been expressions of discontent from other quarters.
The Russian foreign minister, Sergei Lavrov, also questioned the legality of the air strikes, suggesting the UN peacekeepers may have overstepped their mandate to be neutral.
The chairman of the African Union declared that foreign military intervention was unjustified.
Having recently demonstrated in Libya an increased willingness to use military force in internal conflicts, the UN has to take such concerns seriously.
In this case, as in Libya, the Security Council says it has a responsibility to protect civilians targeted by parties to the conflict. But the resolution on Ivory Coast adopted last week was unusually specific. It sanctioned "all necessary means... to prevent the use of heavy weapons against the civilian population."
Strong Council support
That this led to air strikes on Mr Gbagbo's rocket launchers should not have been a surprise to anyone, says Colin Keating of the UN watchdog Security Council Report.
He says the operation is clearly legal as long as it's protecting civilians and UN peacekeepers already had a mandate to use force to do so.
"The whole purpose of the resolution by its sponsors was not to authorise [force] but to actually encourage its implementation," says Mr Keating
Alain Le Roy, head of UN peacekeeping operations, agreed, stressing the strong political backing of the Council, which adopted the resolution unanimously, and the growing threat from heavy weapons. He said Mr Gbagbo's forces had sharply escalated the shelling of both civilians and the UN in the days leading up to the air strikes.
"If heavy weapons had not been shelling us and civilians in the last three days, we would not have undertaken this operation," he told journalists.
But although the resolution is cast in neutral language, a UN official admitted the effect of the air strikes was to seriously degrade the military capacity of pro-Gbagbo forces, which include the national army.
And the strikes were carried out as fighters loyal to Mr Gbagbo's rival, Alassane Ouattara, launched what they called a "final assault" on the incumbent president's last stronghold in the economic capital of Abidjan.
The Security Council has recognised Mr Ouattara as the winner of disputed elections and slapped sanctions on Mr Gbagbo to try to force him to cede power. But it is jittery about any suggestion that it has joined the fight on Mr Ouattara's side.
During a private Council briefing diplomats said Mr Le Roy was bombarded with questions about reported strikes on the presidential palace, which would clearly be outside the mandate of protecting civilians. The peacekeeping chief assured them the target was heavy weapons in the area, not the palace itself, but the unease remains.
"We support the mandate of protecting innocent lives," said an African diplomat, "but we're worried about whether the resolution is being strictly implemented. It's difficult to say because we don't have clear information in terms of what has been targeted."
The participation of France's military has also muddied the waters for some.
France maintains a 1,600-strong force in Ivory Coast, which is authorised by the Security Council to support the UN mission.
Aware of the sensitivities surrounding its position as the former colonial power, president Nicolas Sarkozy waited for a specific request for help with the air strikes from the UN Secretary General Ban Ki-Moon and, as in Libya, has emphasised that French military action is strictly to support UN efforts to save lives.
However, it was Mr Sarkozy who first floated the idea of banning heavy weapons in Ivory Coast. This, coupled with the leading role France played in advocating force in Libya, was seen by some as part of a more muscular military policy to bolster his domestic standing in an election year.
Protecting or forcing change?
Others, such as Phyllis Bennis of the Washington-based think tank International Policy Studies, says the timing of the operation "strengthens the argument that the air strikes are more of a political than a humanitarian intervention," aimed at helping to "re-establish the French presence in Francophone Africa."
She says the interventions in both Libya and Ivory Coast suggest that powerful forces are once again using the UN as an instrument for their own interests, rather than legitimising it as an institution of international law.
Colin Keating disagrees. Both Libya and the Ivory Coast represent a "slight shift not so much in the Council's willingness to act (to prevent atrocities), but more of an unwillingness to be blamed if things go really badly."
This could have been the case in Abidjan, he says, if heavy weapons had been used extensively in a concentrated urban environment.
What is clear is that if the UN continues to sanction military interventions in national conflicts, there will be continuing questions about whether it is acting to protect civilians, or using humanitarian justifications as a smokescreen to force political change.