Roger Hardy BBC Middle East analyst

It is still unclear who carried out Tuesday's attack in the diplomatic quarter of the Syrian capital Damascus.

A building formerly used by the UN appears to have been targeted

The attack damaged a building formerly used by the United Nations, and left four people dead.

The Syrian authorities have described the attackers as terrorists, but the attack has provoked puzzlement and shock in the region, as well as in Syria itself.

With the demise of the Saddam Hussein regime in neighbouring Iraq, Syria is perhaps the last of the region's Soviet bloc-style police states. Its capital has not experienced serious violence for decades.

Target unclear

But uncertainty remains about just who the attackers were - and just what their intended target was.

The building that took the force of the bomb blast was one used in the past by the United Nations - but several Western embassies are also in the vicinity.

Several Arab commentators are saying that the poison of Iraq - in other words, the crisis triggered by the US-led intervention there - is now infecting the region as a whole

Experts are debating three sets of suspects.

There has recently been violent unrest among Syria's Kurdish minority, which feels badly neglected by the Damascus government. But on the face of it, it seems odd that a domestic group would target foreigners.

Then there is the Muslim Brotherhood, the Islamist group harshly suppressed by the Syrian authorities in the 1980s.

And finally - inevitably - there's the al-Qaeda network and its various affiliates.

Affect on region

Recent attacks in which al-Qaeda is suspected of involvement have been in countries such as Turkey, Saudi Arabia and Morocco - whose governments are close allies of the United States. Syria does not fit that category.

Nevertheless if the intended target was indeed a building associated with the United Nations, the attack comes at a time when the world body is more closely involved than ever in trying to find a formula for Iraq's political future.