Around 170 people were killed last year by suicide bombers in Baghdad and Karbala during Ashura, which is commemorated by Shias. The government said it was taking the emergency measures to prevent a possible repetition. Tensions remain high after the recent elections in which the Shias turned out to vote in force while far fewer numbers of Sunnis - who had been in the ascendancy until the fall of Saddam - went to the polls.
A Shia coalition, organised by Grand Ayatollah Ali al-Sistani, has a significant lead in the votes counted so far and its members are expected to form the core of the new government.
Millions of Shias assemble every year for Ashura, in remembrance of the martyrdom of Imam Hussein in AD680, with many taking part in self-flagellation and mutilation. Many road crossings from Syria, Iran and Jordan are already closed.
Thair al-Naqeeb, the Iraqi interim government's spokesman, said: "We have taken the decision to stop people flooding into Iraq during this time and making the situation dangerous for both themselves and Iraqis."
Meanwhile, violence continued with 10 Iraqi policemen killed in a gun battle with insurgents south of Baghdad. The fighting near Salman Pak, the site of a former arms complex, lasted for several hours and its ferocity prevented the security forces from reaching many of the injured or recovering the dead.
Police officials said that the insurgents were well armed and appeared to have information that enabled them to block off the routes used for reinforcements.
Elsewhere, at least eight Iraqi civilians were killed yesterday, three from a car bomb in central Baghdad where a US Army convoy was thought to be the intended target. South of the capital, police discovered the bodies of 20 drivers who are thought to have been killed on their way to the southern city of Kut on Wednesday.
Iraq's election commission said it was making final checks on about 300 ballot boxes over the next few days and a final result is expected to be announced early next week.