Turkey is becoming a more dangerous place, but then so is the Middle East and North Africa and anywhere Isis can send its suicide squads. The Turkish authorities say that the bomber who killed at least 10 people, mostly German tourists, near the obelisk of Theodosius, not far from Hagia Sophia and the Blue Mosque in Istanbul, was a 28-year-old Saudi making it likely though not certain that Isis ordered the attack.

If Isis was behind the bombing it is important to know if this is a one-off or the start of a new campaign. In July its suicide bombers killed 30 Turks going to help rebuild the Syrian Kurdish city of Kobani and in October they killed a further 100 peace demonstrators outside Ankara railway station.

By doing so, Isis succeeded in setting the political agenda by provoking a resumption of hostilities between Turks and Kurds and setting the scene for President Recep Tayyip Erdogan success in the parliamentary election on 1 November.

In pictures: Istanbul explosion Show all 9 1 /9 In pictures: Istanbul explosion In pictures: Istanbul explosion A carnation is left at the site of the explosion in the historic Sultanahmet district in Istanbul AP In pictures: Istanbul explosion A screen shot of the explosion from a tourist camera, Sultanahmet Square, Istanbul In pictures: Istanbul explosion Rescue teams gather at the scene after an explosion in central Istanbul In pictures: Istanbul explosion Policemen secure an area at the historic Sultanahmet district, which is popular with tourists, after an explosion in Istanbul In pictures: Istanbul explosion Police secure the area after an explosion near the Ottoman-era Sultanahmet mosque, known as Blue mosque in Istanbul In pictures: Istanbul explosion Police investigate the area after an explosion in central Istanbul In pictures: Istanbul explosion Turkish police sealed off a central Istanbul square in the historic Sultanahmet district after a large explosion Reuters In pictures: Istanbul explosion Police secure the area after an explosion in central Istanbul In pictures: Istanbul explosion Policemen secure an area at the historic Sultanahmet district, after an explosion in Istanbul

Isis targets civilian targets with such frequency that it is possible to read too much into a single explosion. It was presumably aimed at Turkey’s $21 billion income from tourism with an implied threat of more to come.

Turkey has been unenthusiastically sending planes to bomb Isis targets in Syria, under pressure from the US, and has arrested members of Isis cells inside Turkey. The government may not have done very much, but this is very different from the years when Isis volunteers were able to cross unimpeded the Turkish-Syrian border to reach the Islamic State.

Much of this border has been closed on the Syrian side by the advances of the Syrian Kurdish forces that now control half the 550-mile-long frontier. The Turkish government has insisted that it will not allow Kurdish forces to advance west of the Euphrates, to close off the last 60-mile long stretch of territory which is Isis’s last access and exit point with Turkey.

Video shows aftermath of Istanbul explosion

The US has been forcefully demanding that Turkey seal this border by stationing 30,000 soldiers on the Turkish side of the frontier, west of Jarabulus. This pressure has been growing since the Paris massacre on 13 November, in the light of evidence that the master-mind of the plot had been able to reach France from the territory controlled by Isis, by crossing easily into Turkey. A possible motive for yesterday’s bombing could be a warning that Isis will retaliate for any measures taken against it by the Turkish state. It certainly has the means to do so, because 1,000 or more of its fighters are Turks and it has pockets of committed support inside Turkey.

The violence emanating from the civil wars in Syria and Iraq has already affected Turkey. Low level guerrilla warfare between the Kurdistan Workers Party (PKK) and the Turkish army is spreading across Kurdish areas of south east Turkey. President Erdogan reinforced his power at home when his party won the parliamentary election. Turkey’s influence in Syria is under threat, however, both from the Syrian Kurds – backed by US air strikes and from Russia’s extreme hostility to Turkey after Turkish jets shot down a one of its aircraft in November, in what looks like a carefully-prepared ambush. Russian military engagement in Syria makes it more difficult for Turkey to threaten to act against the Kurds there.