At least six people were killed and dozens wounded when a suicide car bomber and Taliban gunmen attacked an office of the Afghan intelligence agency in the eastern city of Jalalabad on Saturday, officials said.
Heavy fighting was continuing between the Taliban and Afghan security forces hours after the attack on the Jalalabad headquarters of the National Directorate of Security began, said Ahmad Zeya Abdulzai, a spokesman for the governor of eastern Nangarhar province near the border with Pakistan.
Nangahar's public health director, Najib Kamawal, said: "So far six bodies and 45 wounded have been transferred to the local hospital."
"Most of the victims are civilians," Kamawal said.
Abdulzai said the toll was likely to rise.
The Taliban claimed responsibility for the attack, part of a broader pattern of bold offensives by militants across Afghanistan that has emerged in recent weeks during the summer "fighting season."
The violence coincides with a political deadlock in the capital, Kabul, where rival presidential candidates have been unable to resolve months-long disputes over an election meant to mark the first democratic transfer of power in Afghan history.
Most foreign combat troops are due to leave by the end of the year but the deadlock over the presidential election has meant a prolonged delay in signing a security pact with the United States governing how many troops would remain.
While the political impasse drags on, the Taliban-led insurgency has focused on important tactical and symbolic targets as a challenge to the Afghan security forces who are taking over from their Nato-led counterparts.
Afghan forces have been struggling to fight off large numbers of insurgent fighters in provinces to the east, north and south of Kabul in recent weeks.
"This is part of an alarming trend across the country," said Graeme Smith, a senior analyst at the International Crisis Group in Kabul. "They are longer in duration, bigger in size and against more ambitious targets than we've seen previously."
In northern Kunduz province, security forces were in a standoff with insurgents in a weeks-long battle for control over the province that was the last Taliban stronghold before they were driven out by the U.S.-backed Northern Alliance in 2001.
"The insurgents are better armed than us," said Kunduz police chief Mustafa Mohseni.
"They use heavy machine guns, RPGs (rocket-propelled grenades), and 82mm rockets against our forces," he said.
Another Kunduz police spokesman said security forces were concentrated on a district just next to the provincial capital.
Many Kunduz residents have fled to nearby provinces to escape the violence but those who have stayed behind are fed up.
"There is no job, no security, no life," said Kunduz shopkeeper Sayed Malek. "We don't care if the Taliban come back and take over the whole country. We want a peaceful life."
Hundreds of Taliban fighters have also launched attacks this month in Logar province, strategically located to the south of Kabul.