The arrest of 190 people in Cairo, and the likelihood that they will be hauled before military courts, is designed to send a clear signal to Islamic radicals who would inflame communal violence. Such decisive action on the part of the Supreme Military Council, however, should not be allowed to disguise several uncomfortable facts.

The first is that, since the enforced departure of President Hosni Mubarak, sectarian tensions have grown. The clashes that precipitated the arrests at the weekend resulted in at least 10 people being killed and almost 200 people injured. But they did not come out of nowhere. They were the culmination of a steady increase in incidents between conservative Salafist Muslims and the country's Coptic Christian minority. There was a similar outbreak of violence in another Cairo district in March and the recent appointment of a Christian governor in the southern city of Qena prompted a week of protests.

When a Coptic church in Alexandria was bombed on New Year's Day, local Muslims came together a week later to form a cordon around that and other Christian churches, so that Copts could attend their Christmas services in safety. The same spirit of mutual support and tolerance was evident during the protests on Tahrir Square. This increasingly looks like a deceptively harmonious interlude.

The second is that the recent increase in sectarian clashes has been part of a general decline in law and order that the military authorities have been unwilling or unable to stem. This is fuelling speculation that Islamic extremists or remnants of the Mubarak regime, or both, are fomenting trouble in the hope of reversing the gains that were made.

And the third relates to the short attention span of the outside world. Violence in Libya, unrest in Yemen, and the ruthless suppression of protest in Syria have all claimed attention in recent weeks, allowing the impression of euphoria that followed the successful uprising to linger. Egypt may indeed be a better and freer country than it was, but instability lies only just beneath the surface. The time between now and the September elections could be perilous indeed.