Iraq says it will close its border crossings with Iran and Syria for three days as part of its new security plan for the capital, Baghdad.
The US president has committed to sending 21,500 more troops
Top commander Lt Gen Abboud Gambar used a live TV address to unveil the plan which also extends the Baghdad curfew.
The US-backed security drive is now being debated in the US Congress.
Gen Gambar is in charge of a plan that will divide Baghdad into 10 security districts in an attempt to drive out insurgents and illegal militias.
Meanwhile radical Iraqi Shia cleric Moqtada Sadr has gone to Iran, fearing he might be targeted in the new security push, US officials have said.
Mr Sadr went to Tehran by car several weeks ago, officials are reported as saying.
The officials said they did not believe Mr Sadr, who leads the Mehdi Army militia, had left Iraq for good.
Thousands of extra US troops are heading to the Iraqi capital to bolster Iraqi forces in the new security "surge".
US President George W Bush is committed to sending 21,500 additional troops to Iraq, but he faces strong opposition in the Democratic-led Congress.
Iraq-Syria border: 605km (378 miles). Crossings to close: Rabi'ah and al-Walid
Iraq-Iran border: 1,458km (906 miles). Crossings to close: Al-Shalamijah, Zurbatiyah, Hajj Umran, and Bishmaqh
Gen Gambar, speaking on behalf of the Cabinet and Prime Minister Nouri Maliki, did not say when the border points would close.
Officials told the BBC the curfew in Baghdad would be extended by one hour, starting at 2000 local time (1700 GMT) instead of 2100, and continuing to 0600.
Officials also said that after the 72-hour border closure, the crossing points with Iran would only be partially reopened.
Gen Gambar said the new plan would give him sweeping emergency powers, combining the command of the police and armed forces.
Weapons permits would be restricted to the Iraqi and US military.
The BBC's Andrew North in Baghdad says the Iraqis want to be seen taking the lead on the security drive but a lot of questions have been left unanswered and a lot of scepticism remains.
Lt Gen Abboud Gambar is in charge of the new security plan
The border move comes amid claims by the US that Iran is supplying militias with sophisticated weapons to attack US troops. Tehran rejects the accusation.
Correspondents say it is unclear how the border closure will be effective as the frontiers are long, porous and often barely guarded.
Violence continued in Iraq on Tuesday despite the new security plans.
A van crammed with explosives detonated near a college in western Baghdad, killing at least 16 people and injuring 45.
The attack is the latest in a string of deadly incidents in Baghdad.
On Monday a series of car bombs in markets in the centre of the capital killed at least 76 people and wounded 164.