Turkey yesterday announced a ban on all Syrian flights over its territory in retaliation for an equivalent step taken by Damascus. That move, which was a response by Syria to Turkey's forcing down of a Syrian passenger plane a week before, not only takes regional tensions to a new and still riskier level, but effectively closes one of the remaining air corridors for Syria to the north and west.

It can be argued that relations between Turkey and Syria were already nearing breaking point before the incident of the plane, which Ankara said was carrying illegal arms. Earlier this month, Syrian mortars landed inside the town of Akcakale, the Turkish army fired back, and Ankara authorised troops to enter Syria in the event of a repetition.

In general, though, Turkey has shown commendable restraint in responding to a crisis on its borders that is not of its making. With minimum complaint, it has sheltered 80,000 Syrian refugees, despite the cost and destabilising effect on its own population. After the attack on Akcakale, which killed five Turkish citizens, Ankara engaged in a night of retaliatory shelling and passed the provision on intervention through its Parliament, but took no further action. While it was forthright in its condemnation, it did not ask Nato to invoke Article 5.

This relative restraint made its decision to intercept a Syrian civilian plane on its way from Moscow particularly problematical. Syria denied that the plane was carrying weapons. Russia, after a delay, said the cargo was legal radar equipment. But there are two points here. The first is whether Moscow should be supplying Damascus with equipment that has a clear military use, even if it is technically legal. The second is Turkey's failure to provide any evidence of illegal weapons.

Ankara took a big risk in forcing down a civilian aircraft. If there were no actual weapons, this casts doubt on the quality of both its intelligence and its decision-making. None of this inspires confidence at such a sensitive time.