The leaders of five Central Asian countries gathered for talks in Turkmenistan on Friday, with the spiral of war in neighbouring Afghanistan topping their agenda as US-led forces lave the country.

The talks in the Caspian Sea town of Avaza come as the Taliban challenges Afghan government forces in several large cities after weeks of gains in the countryside, including in provinces next to the three former Soviet 'stans' that border the country -- Tajikistan, Turkmenistan and Uzbekistan. 

Turkmen president Gurbanguly Berdymukhamedov called Afghanistan "the question that worries all of us" on Wednesday as state television showed him receiving his Tajikistan counterpart Emomali Rakhmon for bilateral talks ahead of the summit. 

Russia, meanwhile, was involved in joint military drills close to Afghanistan's borders in both Tajikistan and Uzbekistan as a top Kremlin military official flew into the region Thursday to observe the exercises and hold talks.

Fighting in Afghanistan's long-running conflict began to intensify in May, when US and other foreign forces began the withdrawal due to be completed later this month.

In June, the Taliban captured Afghanistan's main crossing with Tajikistan, Shir Khan Bandar, while Kabul's troops have been forced to retreat into both Tajikistan and Uzbekistan in recent weeks during heavy fighting with the group. 

The Taliban has insisted that it has no designs on Central Asia, and has established official contacts with both Uzbekistan and Turkmenistan as it casts itself as a government-in-waiting. 

But analysts argue that a growing security vacuum in the country can pose its own threat to Central Asia, as well as the region's growing economic cooperation with Kabul.

Valery Gerasimov, chief of the Russian military's General Staff, arrived in Uzbekistan for talks Thursday, and to observe military drills that are expected to wrap up next week. 

During a meeting with Uzbek counterpart Shukhrat Khalmukhamedov, Gerasimov said the drills took place "to practise actions to repel terrorist threats".

"The main threat to the Central Asian region today comes from the Afghan direction," Gerasimov said, noting that Moscow was increasing its supplies of weapons to the region.

The annual summit being held in Avaza is a rare instance of the Central Asian states convening for talks without powers from outside the region, such as Russia, China or the United States.