By Humphrey Hawksley
Yemen is fertile ground for al-Qaeda
The increased violence in Yemen is a clear indication that military campaigns to crush al-Qaeda-inspired violence extend far beyond the borders of Afghanistan and Pakistan.
It also shows up hostile fault-lines within the Middle East, pitting mainly Shia Iran against Sunni Saudi Arabia, who condemn each other for taking sides in Yemen's long-running civil war.
Yemen is one of the poorest countries in the Arab world with almost half its 24 million people living below the poverty line and an authoritarian government that has failed to win the trust of a substantive part of its own population.
This makes fertile ground for al-Qaeda.
US intelligence agencies have determined that, along with Pakistan, Yemen is a key area on which to concentrate on al-Qaeda.
More than 90 detainees still in America's Guantanamo Bay detention centre come from Yemen. That is nearly half the total.
Despite the policy to close Guantanamo, US authorities do not want to send them back for fear that they would boost al-Qaeda's operations and morale there.
The US has invested some $70m (£40m) in military aid in Yemen in the past year, believed to include training, the use of drones and intelligence to pinpoint al-Qaeda camps and activity.
Much is classified because neither Yemen nor the US wants American activities there to stir up yet more dissent.
The instability in Yemen is becoming critical. Al-Qaeda has announced that its networks in Yemen and Saudi Arabia have merged to create al-Qaeda in the Arabian Peninsula.
The civil war is being waged by the Shia community in the north that borders Saudi Arabia. Saudi forces have actively intervened.
In one case it was accused of bombing a market killing many civilians.
Iran has publicly warned against any foreign intervention.
And - although the phrase is now frowned upon - US intelligence agencies are keeping a closer and closer watch in this newly-emerging theatre in the "war on terror".