KABUL, Aug 15 (Reuters) - Afghanistan's Taliban on Tuesday marked the second anniversary of their return to power, celebrating their take-over of Kabul and the establishment of what they said was security throughout the country under an Islamic system.

After a lightning offensive as U.S.-led foreign forces were withdrawing after 20 years of inconclusive war, the Taliban entered the capital on Aug. 15, 2021, as the U.S.-backed president, Ashraf Ghani, fled and the Afghan security forces, set up with years of Western support, disintegrated.

"On the second anniversary of the conquest of Kabul, we would like to congratulate the mujahid (holy warrior) nation of Afghanistan and ask them to thank Almighty Allah for this great victory," the spokesman for the Taliban, Zabihullah Mujahid, said in a statement.

Security was tight in the capital on Tuesday, which was declared a holiday, with soldiers stepping up checks.

Taliban parades were expected through the day and several departments, including the education ministry, held gatherings to celebrate.

"Now that overall security is ensured in the country, the entire territory of the country is managed under a single leadership, an Islamic system is in place and everything is explained from the angle of sharia," Mujahid said.

Afghanistan is enjoying peace not seen in decades but the U.N. says there have, nevertheless, been dozens of attacks on civilians, some claimed by the Islamic State rivals of the Taliban.

For many women, who enjoyed extensive rights and freedoms during the two decades of rule by Western-backed governments, their plight has become dire since the return of the Taliban.

"It's been two years since the Taliban took over in Afghanistan. Two years that upturned the lives of Afghan women and girls, their rights and futures," Amina Mohammed, deputy secretary-general of the U.N., said in a statement.

Mujahid made no mention of the contentious issue of female education in his statement.