Taliban militants clashed with police in the same district where 23 South Koreans were abducted by Afghan insurgents, police said Wednesday. Four militants were killed and six wounded.

The militants withdrew after exchanging fire for about an hour with police at a checkpoint in Qarabagh district of Ghazni province on Tuesday, said Mohammad Zaman, the deputy provincial police chief. He said no police were hurt in the clash.

The 23 South Koreans were abducted July 19 in Qarabagh as they traveled by bus from Kabul to the southern city of Kandahar. Two of the captives have since been killed by the Taliban.

There was no immediate indication that Tuesday's clash was linked to the hostage crisis.

There has not yet been a breakthrough in negotiations almost three weeks into the hostage ordeal. The captives — volunteers from a church group who planned to do health work in Afghanistan — include 16 women and five men.

The Taliban are demanding that Afghan authorities and the U.S. military release a number of militant prisoners in return for freeing the South Koreans. Afghan authorities have so far refused any exchange, fearing it could lead to more kidnappings, despite South Korea urging "flexibility" in the case.

Elsewhere, a group of 75 Taliban militants tried to overrun a U.S.-led coalition base in southern Afghanistan on Tuesday, a rare frontal attack that left more than 20 militants dead, the coalition said in a statement.

The insurgents attacked Firebase Anaconda from three sides, using gunfire, grenades and 107 mm rockets, the coalition said. A joint Afghan-U.S. force repelled the attack with mortars, machine guns and air support.

"Almost two dozen insurgents were confirmed killed in the attack," the statement said. Four girls aged 2 to 12 and two Afghan soldiers were wounded during the fight in Uruzgan province, it said.

A firebase like Anaconda is usually a remote outpost staffed by as few as several dozen soldiers.

"The inability of the insurgent forces to inflict any severe damage on Firebase Anaconda, while being simultaneously decimated in the process, should be a clear indication of the ineffectiveness of their fighters," said Army Capt. Vanessa R. Bowman, a coalition spokeswoman.