Five police officers and four civilians died in the attack in Dund district, about 10 miles south of Kandahar city, said Zalmay Ayubi, the spokesman for Kandahar's governor.
Canadian soldiers and Afghan police stood guard at the blast site and ordered journalists not to take photos, according to an Associated Press reporter at the scene. A spokesman for NATO's International Security Assistance Force said he would investigate the report.
The Canadian soldiers refused to let Afghan police approach the blast site, the reporter said.
Kandahar is the spiritual birthplace of the Taliban and continues to be a militant stronghold. Afghan police frequently suffer from Taliban attacks from roadside and suicide bombs.
Meanwhile, attackers armed with assault rifles and hand grenadesin eastern on Monday, triggering a shootout that killed as many as 22 officers in the same area where Sri Lanka's cricket team was ambushed less than a month ago.
A roadside bomb also killed three police in Afghanistan's eastern province of Paktia on Monday, the Interior Ministry said.
Taliban attacks have spiked the last three years, as militants have taken control of wide swaths of countryside. President Obama is sending 21,000 additional American troops to bolster the record 38,000 already in the country.
President host Bob Schieffer on Sunday that America needs, "to refocus attention on al Qaeda. We are going to root out their networks, their bases. We are gonna make sure that they cannot attack U.S. citizens, U.S. soil, U.S. interests, and our allies' interests around the world."
Mr. Obama told Schieffer his administration's new plan for tackling militants in Pakistan and Afghanistan, "does not change the recognition of Pakistan as a sovereign government. We need to work with them and through them to deal with al Qaeda. But we have to hold them much more accountable."
Officials from more than 70 countries are attending a conference in the Netherlands on Tuesday focusing on Afghanistan. The United States, which announced a new strategy for Afghanistan and Pakistan last week that will focus on fighting al Qaeda, is expected to explain its policies for the region.