The death toll of a market explosion Tuesday has risen to 51 with 75 injured, local police said.

The explosion at about 5:45 P.M. (1445 GMT) targeted a parking lot crowded with mini buses near a bustling market in the Shiite al-Uriya district, a police source said on condition of anonymity.

Earlier in the day, a suicide motorcycle bomber struck an anti-Qaida group checkpoint in northern Baghdad, killing four fighters and wounding two civilians.

The car bombing was the deadliest in Baghdad since March 6 when a market was hit by bombs, nearly 70 people died and more than a hundred were injured.

Tuesday's car bomb attack came as a grisly reminder of the volatility of the country's security situation as violence has fallen to its lowest level in four years.

Violence has been dropping on the whole in Baghdad as well as most of the country since last summer.

The decline was largely attributed to the reinforcement of US troops, the ceasefire of major Shiite militia and the insurgency of Sunnis against al-Qaida.

But the US military warned that security remains fragile and the gain is reversible.

(Xinhua News Agency June 18, 2008)