A delegation of U.S. senators visiting Iraq has expressed regret about a U.S. court's decision to drop charges against American security contractors accused of killing Iraqi civilians in 2007.

Republican Senator John McCain said in Baghdad Tuesday the senators hope the ruling will be appealed.  He also expressed sympathy for the families of those killed in the incident.

Five guards - employees of the company Blackwater - were charged with opening fire on unarmed civilians at a Baghdad intersection, killing 17 people. 

A U.S. judge dismissed charges last week against the guards, saying the U.S. government had violated their constitutional rights.

The Senate delegation, which includes independent Senator Joe Lieberman and Republicans John Barrasso and John Thune, met Tuesday with Iraqi Prime Minister Nouri al-Maliki and President Jalal Talabani.

Speaking at the news conference, Senator Lieberman said the United States plans to maintain a "significant military presence" in Iraq through elections in March, to discourage attempts to disrupt the vote.

Lieberman also said the top U.S. commander in Iraq, General Ray Odierno, told the visiting senators that plans to withdraw American troops from Iraq are on track.

Washington plans to reduce the number of U.S. troops in Iraq from 115,000 to 50,000 by August of next year, and to withdraw all forces by 2011.

Some information for this report was provided by AFP.