KABUL (AFP) - Three people have been arrested over an attempt to shoot down President Hamid Karzai's helicopter during an election campaign visit to southeast Afghanistan, an interior ministry spokesman said.

The three were detained at a village some nine kilometres (5.5 miles) from the scene of the attack near the southeastern town of Gardez, spokesman Lutfullah Mashal told AFP.

"They had documents and tools related to the rocket attack and were arrested by police with the help of villagers," he said.

Karzai's first visit to southern Afghanistan during the election campaign was aborted after a rocket was fired at his helicopter. The rocket missed its target and landed near a school without causing any casualties.

The three Afghan nationals were not from the area and were hiding in the village, the spokesman said.

Separately, the US military confirmed that a rocket was fired at a helicopter carrying Karzai as he arrived in Gardez to open a road and speak at a high school.

"A rocket was fired at a helicopter while it attempted to land near Gardez . The rocket missed the helicopter, carrying President Hamid Karzai, and impacted approximately 300 meters away from a school near the landing zone," the US military said in an e-mailed statement late Thursday.

"The aircraft did not land and flew immediately back to Kabul. The president was not in any imminent danger. No one was injured in the incident," the statement said.

The attack came as Washington said about 1,100 troops from the elite 82nd Airborne Division are being deployed to Afghanistan to beef up security for the October 9 presidential elections.

The extra troops, which will be added to the 15,500 US troops already in the country, will deploy "very soon," a defense department official said on condition of anonymity.

"It will be about 1,100 troops, " she said. "They are going there to augment security operations."

The Bush administration has touted the elections as evidence of progress since US forces drove the Taliban from power in 2001.

But military commanders expect stepped up attacks by Taliban and al-Qaeda forces to disrupt balloting.