The "multi-pronged attack" targeted a police station in the city of Jalalabad
At least four people have died after a suspected suicide attack on a police station in eastern Afghanistan.
Police officials in the city of Jalalabad say gun battles started after a "multi-pronged" attack by insurgents.
Reports suggest a suicide car bomber targeted the police station, together with around five gunmen.
A spokesman for the governor of the Nangarhar province said the battle was continuing four hours after the early morning attack started.
The insurgents are believed to have stormed the key police station in the heart of the city, close to government offices and the headquarters of the governor.
Sediq Sediqqi, spokesman for the interior ministry, said that five militants had been killed and the remaining attackers remained holed up inside the police station.
Witnesses and rickshaw drivers in the city told the BBC that the state-run Radio Television Afghanistan was one of many buildings that were still on fire following the attack.
A senior police official in Nangarhar told the BBC: "There is serious fighting going on between police and the attackers right now."
Mohammad Habib, an eyewitness, said the explosion shook the city.
"I woke up and my windows were broken than there were gun shots and explosions through out the morning. Now almost half of the city remains closed," he said.
A local taxi driver Khan Jan told the BBC: "The sound of the explosion was deafening, there was a powerful explosion which broke windows of nearby shops and homes. It woke the city."
On Tuesday, a suicide attack in northern Afghanistan killed 17 civilians including women and children and injured more than 60.
The attacks come as Afghans prepare to hold presidential elections on 5 April. The Taliban have vowed a campaign of violence to disrupt the vote.