Militants fired mortars at Baghdad's heavily fortified Green Zone Tuesday, hours after U.S. Vice President Joe Biden arrived in the Iraqi capital.
Police say the attack killed two civilians and wounded five others in a nearby apartment building.
Biden met Tuesday with U.S. Ambassador Christopher Hill and the top U.S. commander in the country, General Ray Odierno.
The vice president said General Odierno is optimistic Iraqi forces will be ready on schedule to allow U.S. troop withdrawals to proceed as planned. The United States is taking steps to withdraw all combat troops from Iraq by August 2010.
Biden said Iraq's national elections in January were key to resolving political differences between the country's Kurdish, Shi'ite and Sunni communities.
Violence has dropped significantly in Iraq this year, but there have been recent sectarian attacks.
Prime Minister Maliki has accused supporters of Saddam Hussein's banned Baath party based in Syria of plotting two truck bombings that killed nearly 100 people in Baghdad last month.
On Tuesday, General Odierno there are some "expat settlements" inside Syria that are funding operations inside Iraq. He said Syria must take action against the elements that encourage attacks inside Iraq.
Biden is expected to meet with Iraqi Prime Minister Nouri al-Maliki, President Jalal Talabani and the president of Iraq's autonomous Kurdish region, Massoud Barzani, while in Iraq.
The U.S. vice president has been assigned to oversee the Obama administration's policy in the country, and has visited Iraq three times this year.
Some information for this report was provided by AFP, AP and Reuters.