KUNDUZ, Afghanistan (Reuters) - Taliban fighters seized a district in the northern province of Baghlan on Tuesday and kept up pressure on the central city of Ghazni as heavy fighting continued across Afghanistan following the start of the insurgents’ annual spring offensive last month.

Police officials said security forces had abandoned the district center of Tala-wa Bafrak after becoming cut off from supplies during days of fighting.

“The Taliban have been attacking the district for a few days and at 11 a.m. we had to retreat,” said provincial police spokesman Zabihullah Shuja.

The loss follows Taliban pressure last week on the northern province of Badakhshan, where the insurgents took control of a district center and have been battling government forces who claimed to have retaken it.

In Ghazni province, south of the capital Kabul, government forces backed by air strikes have been battling for control of a key highway and fierce fighting continued on Tuesday, with the Taliban saying it had killed more than 100 government troops.

Mohammad Zaman, police chief of Ghazni said five Taliban militants were killed and their bodies were left at the site of the attack.

Security officials said around 100 Taliban fighters had been killed in clashes in four provinces over the past 48 hours, with heavy fighting also seen in Faryab province in the northwest.

Estimates of enemy casualties on both sides in the Afghan conflict are often inflated but the numbers point to heavy fighting, underlining the challenge for the government as it prepares for parliamentary elections in October.

Dozens of people have been killed in suicide attacks in Kabul in recent weeks, including some 60 people at a voter registration center and nine journalists in a blast on April 30.

The elections are seen as a key test of the government’s credibility and require millions of voters to register at vulnerable election centers across the country.

In addition to the attack in Kabul, at least 17 people were killed by a blast at a mosque that housed a voter center in the eastern province of Khost last week.

A military spokesman said 66 Taliban militants had been killed and 28 injured during ongoing operations in five districts in Baghlan and Faryab provinces.

In Nangarhar, an eastern province, officials said 19 suspected Taliban militants, including seven Pakistani citizens, were killed in clashes with special forces units, Attaullah Khogyani, the provincial governor’s spokesman said.