The rest of the country saw a surge in violence. Officials said several clashes in Afghanistan's south and east killed 73 Taliban fighters and five private security guards, while a roadside blast killed 10 policemen.
The Interior Ministry said the beefed-up police force in the capital would search buildings as well as cars to "create an environment of trust and prevent any disruptive actions by the enemy."
The security increase comes a day before the country celebrates the 89th anniversary of its independence from Britain. Any breach of security during the celebration would be an embarrassment for President Hamid Karzai's government.
In April, gunmen fired on Karzai at a military parade in Kabul, killing three people, including a lawmaker.
Ministry spokesman Zemarai Bashary said more than 5,000 extra police had been drafted for what he described as the biggest operation of its kind in Kabul since 2001, when U.S.-led forces ousted the Taliban government.
Teams of police stopped vehicles at checkpoints around the city. Kabul so far has been spared the drumbeat of violence that has afflicted other parts of the country, though it suffered spectacular bomb attacks this year against an international hotel and the Indian Embassy.
Bashary declined to discuss whether officials are worried that militants are now at the city's gates.
However, a string of recent high-profile attacks indicate how the resurgent Taliban and other militant groups have gained a foothold in neighboring provinces.
In an ambush last week, insurgents wielding assault riffles gunned down three female aid workers about an hour's drive south of Kabul.
To the west, insurgents have been regularly attacking U.S.-led coalition and NATO supply convoys, burning fuel trucks and killing NATO and coalition soldiers. To the east, the Tag Ab valley of Kapisa province has become the scene of near-daily clashes and air strikes by the U.S.-led military coalition.
Afghan and NATO officials insist that the nearly seven-year effort to bring stability to Afghanistan is progressing.
However, the security operation in Kabul is the second time this year that authorities have taken extraordinary measures to reassure Afghans that the Taliban are not able to assail a major city.
In June, Afghan and NATO commanders scrambled thousands of troops to clear militants from a strategic valley within striking distance of Kandahar, Afghanistan's main southern city.
Overall, insurgent attacks jumped by 50 percent in the first half of 2008, according to recent data from the Afghanistan NGO Safety Office, a Kabul-based group that advises relief groups on security.
More than 3,200 people - mostly militants - have been killed in insurgency-related violence this year, according to an Associated Press count based on figures from Western and Afghan officials.
Most of the violence still takes place in the south and east, where Taliban sympathies run strongest and militant bases in neighboring Pakistan are closer at hand.
In the latest violence: