Officials said insurgents had seized more than a dozen local radio and TV stations in Lashkar Gah -- capital of Helmand province and the scene of days of fierce fighting -- leaving only one pro-Taliban channel broadcasting Islamic programming.

At least 40 civilians were killed and more than 100 wounded in the last 24 hours in Lashkar Gah, the UN Assistance Mission for Afghanistan said Tuesday.

"Deepening concern for Afghan civilians... as fighting worsens," UNAMA tweeted. "UN urges immediate end to fighting in urban areas."

In Herat, another city under siege, hundreds of residents chanted "Allahu akbar" (God is greatest) from their rooftops after government forces repulsed the latest Taliban assault.

The hardline Islamist group has seized control of much of rural Afghanistan since foreign forces began the last stage of their withdrawal in early May, but are meeting resistance as they try to take provincial capitals.

That urban fighting, however, is taking its toll on civilians.

"Taliban ground offensive & ANA air strikes causing most harm," UNAMA said earlier Tuesday, referring to the Afghan national army.

"Deep concerns about indiscriminate shooting & damage to/occupation of health facilities & civilian homes."

"Fighting was intense this morning," said Sefatullah, director of Sukon radio in the city.

"The US B52 and Afghan air force both pounded the Taliban positions," he said, adding that fighting was ongoing near the city's prison and a building housing the headquarters of police and intelligence agencies.

On Monday, the Ministry of Defence said that US air force had carried out air strikes in Lashkar Gah.

In recent days the US military has intensified air strikes across the country in a bid to stem Taliban advances.

Sefatullah said his radio station had "stopped broadcasting two days ago because the Taliban captured the building of our station."

Afghan officials said that 10 other radio and four television stations in Helmand had been seized by the Taliban, most in the provincial capital.

"Terrorists do not want the media to publish the facts and expose their injustices," the Ministry of Information and Culture said.

The loss of Lashkar Gah would be a massive strategic and psychological blow for the government, which has pledged to defend cities at all costs after losing much of the rural countryside to the Taliban over the summer.

In Herat, Afghan officials said government forces had managed to push back the insurgents from several areas of the city -- including near the airport, which is vital for resupplies.

"Afghan security forces plus resistance forces launched a big operation in west of the city," Jailani Farhad, spokesman for Herat's governor, told AFP.

Another official said the US had carried out air strikes in Herat last night.

- 'War crimes' -

Washington and London lashed out at the Taliban, accusing them of committing atrocities that may amount to "war crimes" in the town of Spin Boldak, which the insurgents captured last month along the border with Pakistan.

Afghanistan's Independent Human Rights Commission earlier said the insurgents had indulged in revenge killings there, leaving at least 40 people dead.

"The Taliban chased and identified past and present government officials and killed these people who had no combat role in the conflict," the group said.

Top US diplomat Antony Blinken also slammed the militant leaders.

An Afghanistan without a democratic, inclusive government would be a "pariah state," he said, adding that the international recognition the group wants will not be possible if "seeks to take the country by force and commits the kind of atrocities that have been reported."

Fighting across the country, meanwhile, has displaced around 80,000 children from the start of June, humanitarian organisation Save the Children said Tuesday, adding that many schools and health facilities had also been damaged.