Libya campaign: Could Nato mission unravel?
Two days and two incidents involving civilian casualties. Could this be the moment when support for Nato's Libyan air campaign begins to unravel?
The episode early on Sunday morning when a bomb or missile from a Nato aircraft struck a residential neighbourhood in northern Tripoli appears clear-cut.
A Nato spokesman has expressed the alliance's regret at the loss of civilian lives, suggesting a "weapons system failure" may have caused the incident.
Despite the advanced technology and, in general terms, the great accuracy of much modern weaponry, there is still a great deal that can go wrong.
A bomb can "hang" momentarily under an aircraft rather than being released cleanly.
Fins intended to help steer the weapon may not deploy properly.
There can be faults too with sensors that supply information to the weapon's guidance system.
Such problems are rare. Indeed, this is the first example in this campaign where civilians have been killed and Nato has accepted that something had gone wrong.
Of course, quite apart from mechanical or electro-optical failures, the choice of target can simply be wrong.
Nato has admitted that last week, one of its jets accidentally hit a military vehicle carrying rebel fighters - not the first time, amidst the uncertain battle lines, that Nato has found difficulty in discriminating between Libyan government and opposition forces.
This brings us to Monday's incident - the levelling of a building some 80km (50 miles) from Tripoli, near the town of Sorman in the far north-west of the country.
It is said to be the country home or compound of a senior member of Colonel Muammar Gaddafi's regime.
The BBC's Middle East Editor, Jeremy Bowen, was taken to the site and saw the remains of a young boy being removed from the devastated building.
Nato says that "in the early hours of Monday 20 June [its] warplanes carried out a precision air strike against a key Gaddafi regime command and control node in the vicinity of Zawiya to the west of Tripoli. "
In translation - this was some kind of headquarters.
Nato says it carried out "a rigorous analysis" of the target and "conducted persistent information surveillance reconnaissance over a prolonged period of time in the area prior to the strike".
In plain English, they had been watching the location for some time.
After some hours of delay, a Nato spokesman in Naples told the BBC that after a detailed review of recent operations, the location hit - the one reporters were taken to - was in their view a legitimate military target.
Nato has insisted all along that its air operations are explicitly in support of UN Security Council resolution 1973, intended to protect the civilian population in Libya.
But there has long been some unease in certain quarters within Nato about the Libya mission.
This has consistently been papered over, with all nations agreeing to extend the mission for a further three months from the end of June.
But is this fragile consensus going to be undermined if incidents of civilian casualties increase?
The alliance is already in a sense riding two horses. On the one hand, its operations are aimed at protecting civilians from attacks by Col Gaddafi's forces.
In an expansive reading of the Security Council resolution, this has encompassed attacks on Col Gaddafi's own compound, seen as a legitimate military command and control facility.
Nato spokesmen insist this is not a manhunt to get the Libyan leader.
But leaders from several key Nato countries have made it crystal-clear they want to see the back of Col Gaddafi.
So is the explicit goal the protection of civilians, but with an implicit goal of regime change? Nato still says no.
If civilian casualties begin to mount there's a danger that enthusiasm within the alliance for prolonging the mission could begin to wane.
The conflict has gone on for much longer than many people imagined it would.
The Gaddafi regime has proved more resilient and the rebel forces less able than many predicted.
Nato has embarked upon a difficult course that looks set to get bumpier as the days and weeks go on.