A spate of assaults by suspected Taliban rebels killed four policemen and wounded an election candidate, and Afghanistan warned Sunday that aid workers and other "soft" targets were in danger of attack ahead of elections this month.

The warning came after a string of kidnappings that left a British engineer and two Japanese teachers dead. Five Afghans, including a district governor and an election candidate, were also kidnapped last week. A purported Taliban spokesman claimed to have killed them, though the claim couldn't be independently confirmed.

Interior Ministry spokesman Latfullah Mashal said he was confident the Sept. 18 legislative elections would be successful even though "al-Qaida and the Taliban will try their best to disrupt peace and stability."

"We believe that this will not affect the overall security situation," he told The Associated Press. "They (militants) focus on soft targets attacking candidates, burning schools, aid workers. But the security workers have also taken necessary measures to provide needed security."

Fighting in the past six months has left more than 1,100 people dead and raised fears that the Taliban may manage to disrupt the polls, the next key step toward democracy after decades of fighting.

An assault on a convoy of trucks carrying supplies to a U.S. base in southern Zabul province killed three policemen guarding it, said local government chief Rozi Khan.

The trucks were forced to flee to the safety of the nearby city of Qalat after being ambushed, he said.

Rebels also attacked a police checkpoint on the main road from the southern city of Kandahar to the capital, Kabul, on Saturday, triggering a two hour gunbattle that left one officer dead and two wounded, said local police chief Ghulan Nabi.

Some insurgents were also believed killed in the fighting, but it was unclear how many because the rebels took the bodies with them when they fled, he said.

Also in the south, in Helmand province, a bomb blew up Sunday outside the home of election candidate Hadidullah Khan, said local police chief Din Jan Khan.

He said the candidate was rushed to hospital where doctors amputated his right leg. The police chief blamed the Taliban for the attack.

At least four candidates and four election workers have been killed in recent weeks.

Police said Sunday they could not confirm that an election candidate, as well as the district governor and three others kidnapped Friday, had been killed by the Taliban, as the rebels' purported spokesman claimed.

Meanwhile, some details started to emerge of the abduction of Briton engineer David Addison, whose body was found Saturday by American commandos during a rescue operation.

Mashal, the Interior Ministry spokesman, said the kidnappers killed him immediately after abducting him Wednesday and taking him to a mountain hide-out in western Farah province.

Addison was working for a foreign company building a road from Kandahar to the western city of Herat.