GARDEZ, Afghanistan (Reuters) - Taliban insurgents overran a district in eastern Afghanistan, killing and wounding dozens of police and soldiers and threatening strategically important road routes to Pakistan, officials said on Saturday.

Abdul Rahman Solamal, governor of Jani Khel district, in the eastern province of Paktia said that after heavy overnight fighting, security forces had pulled out of the district, which sits at an intersection linking eight districts and which connects Paktia with neighboring Khost province and Pakistan.

"Our district was surrounded by Taliban for almost five days," he told Reuters. "Hundreds of them attacked our check posts overnight.

"If we do not retake it soon then Taliban can easily move from one province to another and can undermine security in at least three provinces," he said.

The attack comes amid heavy fighting in other parts of Afghanistan, notably in the southern province of Helmand, where U.S. military advisers have been deployed to bolster the defenses, and around the northern city of Kunduz, which fell briefly to the insurgents last year.

More than 20 soldiers and police were killed and another 20 wounded in the fighting overnight, while some 200 Taliban insurgents were killed, Solamal said. There was no immediate means of verifying the claims of Taliban casualties.

Taliban spokesman Zabihullah Mujahid said in a statement dozens of Afghan soldiers and police had been killed in Jani Khel and large amounts of equipment had been captured, including armored vehicles, light and heavy weapons and ammunition.

According to U.S. estimates reported in July by the Special Inspector General for Afghanistan Reconstruction (SIGAR), a Congressional oversight body, Afghan forces control or influence just under 66 percent of the national territory, down from just over 70 percent at the start of the year.

The reduction was partly due to security forces pulling back from exposed areas and concentrating their strength, but after a lull following the death of former leader Mullah Akhtar Mansour in May the Taliban have stepped up their summer offensive.

Some 36 of the 407 districts in the country were under insurgent control or influence, while another 104 were deemed "at risk", SIGAR said.

(Reporting by Samihullah Paiwand, additional reporting by Mirwais Harooni in Kabul; writing by James Mackenzie; Editing by Stephen Coates)