Russia's embassy in Kabul said on Monday it was laying on extra evacuation flights from Afghanistan, while Russian troops carried out military drills close to the Afghan border amid heightened regional security risks.

It was not clear whether the extra flights would continue past a Tuesday deadline agreed between U.S. President Joe Biden and the Taliban for the withdrawal of the U.S. troops who have led security at the airport since the Western-backed government collapsed.

Russia's embassy remained operational in Kabul after Western diplomats rebased to the airport following the Taliban takeover of the capital on Aug. 15.

President Vladimir Putin's special representative on Afghanistan, Zamir Kabulov, said on Monday the embassy was working to establish relations Afghanistan's new Taliban rulers.

Russia was ready to help rebuild Afghanistan's economy, he said, urging Western nations not to freeze the Afghan government's financial assets.

"We are establishing ties (with Taliban officials), our embassy in Kabul is working quite actively on this," he told Russian state television. "We have had such contacts for a long time and we will work further on them."

The embassy said in a series of tweets that extra evacuation flights would be open to Russian citizens and residents as well as nationals of countries in the Collective Security Treaty Organisation (CSTO), a Moscow-led post-Soviet security bloc.

Russia evacuated about 360 people last week and Interfax on Monday quoted a representative of the Afghan disapora centre in Russia as saying 500 Afghans may also be eligible as students, residents or work permit holders.

Meanwhile, Russia's defence ministry said around 500 Russian motorised infantry troops from Russia's military base in Tajikistan were carrying out drills in the mountains near the Afghan border, according to an Interfax report.

The ministry said the drills involved test fire from a S-300 air defence system in a simulated attack on the base.

They are the third set of drills by Russia close to the Afghan border this month. Next month, the CSTO will hold another exercise in Kyrgyzstan which hosts a Russian military airbase.

Russian defence minister Sergei Shoigu said last week Moscow would work more closely with CSTO members as the withdrawal of U.S. forces from Afghanistan raises regional security risks.