Barrages hit Green Zone, gunmen kill seven

* Rocket or mortar fire hits Green Zone

* Gunmen open fire on pedestrians, kill at least 7

* Suicide truck bomber kills 15 Iraqi soldiers in Mosul

By Paul Tait

BAGHDAD (Reuters) - Baghdad's fortified "Green Zone" came under repeated rocket or mortar attack on Sunday, and police said up to eight people had been killed by rockets falling short outside the government and diplomatic compound.

The attacks were part of a wider increase in violence in the capital and in the northern city of Mosul, underlining warnings by U.S. military commanders that recent security gains in Iraq are both fragile and reversible.

In the past, the U.S. military has blamed such attacks on the Green Zone on rogue elements of Shi'ite cleric Moqtada al- Sadr's Mehdi Army militia. Sadr has imposed a ceasefire on the militia, but there have been signs that it is fraying.

In Mosul, a suicide truck bomber killed 15 Iraqi soldiers and wounded 45 people, including civilians, in an attack on an Iraqi army base, the Interior Ministry said. U.S. commanders describe Mosul as al Qaeda's last urban stronghold in Iraq.

Much of Sunday's violence took place in Baghdad, the centre of sectarian bloodletting between Iraq's majority Shi'ites and minority Sunni Muslims in 2006 and 2007 in which tens of thousands died. A security crackdown by U.S. and Iraqi forces has since sharply reduced levels of violence.