Sixty million dollars has been earmarked to tighten control of Iraq's borders and hundreds more vehicles will be deployed to beef up security, said Bremer on Wednesday.
"There are 8000 border police on duty today and more are on the way," said Bremer.
The decision comes a day after at least 169 civilians were killed and more than 500 others wounded in coordinated bombings that rocked the holy city of Karbala and Baghdad.
The attacks, carried out against Shia commemorating Ashura or marking the death of al-Husain, the Prophet Muhammad’s grandson, were the worst attacks in Iraq since the fall of Saddam Hussein.
Iraqi Governing Council President Muhammad Bahr al-Ulum said on Wednesday the toll had reached 271. But Health Minister Khudar Abbas said the confirmed toll was a total of 169, adding that 12 bags of human remains had yet to be identified.
Bremer blamed Jordanian Abu Mussab al-Zarqawi, who is suspected of links to the al-Qaida network, and said his aim was to provoke sectarian violence between Sunnis and Shia.
Meanwhile, top US commander for Iraq General John Abizaid said Washington had intelligence warnings of the Karbala and Baghdad attacks and said they prevented even greater carnage.
IGC president Muhammad Bahr
al-Ulum puts toll above US figure
Abizaid said US and Iraqi forces foiled a third planned attack in Basra and thwarted plans to attack several prominent Shia personalities.
But as Iraqis, numbed by the massive number of deaths, began burying the dead, anti-US sentiments were running high.
"Down, Down America," marchers chanted in Karbala as they streamed down the street, with black flags of mourning waving in the air and coffins, draped in green, the colour of Islam.
"The US military is the cause of our problems," people shouted as they approached the shrine of al-Husain.
The cleric leading funeral prayers in Karbala, Sayyid Saad al-Banna, also criticised the US-led occupation.
"This is all the responsibility of the coalition forces because they are not serious about cooperating with the Iraqi people," said Banna.
Despite the anger towards the occupation, Shia clerics denounced the looming threat of civil war that many believe was the motive for the bombings, which foreign fighters are suspected of carrying out.
"These acts will not pull us to a civil war. In Iraq, there is one Islam with Sunni and Shia," vowed Sayyid Ahmad al-Saafi, a representative of Grand Ayat Allah Ali al-Sistani, the most influential Shia cleric in Iraq.
The US-appointed IGC also said it will delay signing a temporary constitution until Friday, after the three days of national mourning.
Military base targeted
In other developments, three rockets were fired at the headquarters of the US-led occupation late on Wednesday at the same time as Bremer was due to give a news conference, but there were no casualties, said a military spokesman.
"There was a three-rocket attack in the Green Zone at 8:00 pm (1700 GMT)," said the spokesman.
Bremer's appearance was delayed by 45 minutes but it was unclear if this was a result of the attack.
Soldiers in the press centre where Bremer was due to speak
hurried out as the blasts were heard, said an AFP correspondent.
Two other explosions earlier on Wednesday appeared to be controlled blasts, which are regularly carried out by occupation soldiers.