The killing of the US ambassador and three other American officials in Benghazi is, of course, a human tragedy to be roundly condemned. But the violence both there and in Cairo – ostensibly in response to a US-made film that is offensive to Muslims – is also a warning of the fragility of post-Gaddafi Libya and across the countries of the Arab Spring.

The trailer for film-maker Sam Bacile's Innocence of Muslims, posted on the internet, is indeed highly inflammatory, portraying the Prophet Mohamed in gratuitously insulting terms. Even so, it need hardly be said that the activities of a few, deliberately provocative, individuals cannot justify the deaths of Chris Stevens and his colleagues, nor even the demonstration outside the US embassy in Cairo that saw the Stars and Stripes torn down.

But this week's events are not about justification. Just as Mr Bacile (now in hiding) and his main backer (that same US pastor whose threats to burn the Koran sparked deadly rioting in Afghanistan in 2010 and 2011) are exploiting global tensions for their own narrow ends, so too are those Islamists who would use their activities as an excuse for violence.

Sad to say, the fallout does not end here. This week's events not only reveal the deep anger at and distrust of the US across the Islamic world; they also give a glimpse of the forces of instability and extremism long held in check by the dictators toppled by last year's wave of revolutions.

Libya's President Mohammed Magarief apologised for the Benghazi attack, and the Libyan Youth Movement is calling for demonstrations against the group widely blamed for it. But the first death of a US envoy on an overseas posting for more than two decades can only strain relations between Washington and Tripoli.

Thus far, the statements from the White House have remained measured. With the presidential election fast approaching, Mr Obama may be inclined to let domestic political gain be his guide. Given that the stability of much of the Middle East is at stake, he must resist the temptation.