GHAZNI, Afghanistan (Reuters) - Taliban militants captured an important security post outside the central Afghan city of Ghazni on Monday, killing 13 members of government forces and underscoring their vulnerability even in areas where defenses have been bolstered.

The post was part of a belt of strongholds built around Ghazni, which is on the main road between the capital, Kabul, and the Afghan south, after the city was briefly overrun by Taliban in August in one of their biggest offensives in years.

As well as the 13 killed, 13 members of the Western-backed government’s security forces were wounded in the attack, said Arif Noori, a spokesman for the provincial governor.

He said the Taliban had suffered heavy casualties but he had no exact information.

Taliban spokesman Zabihullah Mujahid said in a statement 18 policemen were killed and six wounded and large quantities of weapons and ammunition were seized.

The attack is only the latest indication of the precarious security around Ghazni following the big Taliban assault in August, which shocked the government and was only repelled with the help of U.S. air strikes and special force troops.

A U.S. watchdog agency said last week the Afghan government was struggling to recover control of districts lost to the Taliban while casualties among security forces had reached record levels.

The government had control or influence over 65 percent of the population but only 55.5 percent of Afghanistan’s 407 districts, the agency, the Special Inspector General for Afghanistan Reconstruction, said in a report.

The latest phase of Afghanistan’s decades of war began in late 2001, when U.S.-led troops overthrew the Taliban in response to the Sept. 11 attacks that year on the United States.