Iraqi authorities say they are shortening the nightly curfew in Baghdad - a sign that a U.S.-Iraqi security crackdown is having a positive impact in the capital.

Officials say starting Wednesday the curfew will begin at 10 p.m. local time and last for seven hours, instead of beginning at 8 p.m. local time and lasting for 10 hours.

The crackdown began in mid-February and has been aimed at stopping sectarian violence and disrupting insurgent cells.

Authorities say about 20 people were killed or found dead in Iraq Tuesday.

The U.S. military announced the deaths of four American troops in Iraq, including two killed in combat operations Monday in volatile al-Anbar province.

The military also says coalition forces have killed eight terrorists and detained 13 suspects in an operation in the Arab Jabour area in Baghdad.

A statement says the operation is targeting al-Qaida in Iraq terrorists.

Meanwhile, Iran says one of its top diplomats who was kidnapped in Baghdad nearly two months ago has been freed. Iran's official news agency, IRNA says Jalal Sharafi returned to Iran Tuesday. No other details were provided.

Sharafi, the second secretary at the Iranian Embassy in Baghdad, was abducted by unidentified gunmen wearing Iraqi military uniforms in early February.

Iran blamed the U.S. military for the abduction. The United States denied it was involved.

Some information for this report was provided by AFP, AP and Reuters.