BAGHDAD – Five American soldiers died Monday when a barrage of rockets slammed into a base in a Shiite neighborhood of Baghdad — the largest, single-day loss of life for U.S. forces in Iraq in two years.
The attack follows warnings from Shiite militants backed by Iran and anti-American cleric Muqtada al-Sadr that they would violently resist any effort to keep American troops in Iraq past their year-end deadline to go home

Although American casualties have dropped considerably in the two years since U.S. troops pulled back from Iraq cities, Shiite militias have begun hammering U.S. bases and vehicles with rockets, rocket-propelled grenades and roadside bombs over the past three months.

"Iranian-backed militias are flexing their muscles and have steadily increased military pressure on U.S. forces since rumors first started in the early spring concerning an extension of the U.S. presence," said Michael Knights, an Iraq analyst at the Washington Institute.

In January and February, the U.S. military recorded an average of about three attacks per day. By May, that number jumped to almost six per day. An attack could be anything from a single sniper shot at U.S. troops to a complex attack involving roadside bombs and gunfire.