“Anti-government elements” in Afghanistan attacked the main UN compound in the capital of the western province of Herat on Friday and at least one security guard was killed, the UN Assistance Mission in Afghanistan (UNAMA) said.

The attack, involving rocket-propelled grenades and gunfire, happened hours after Taliban fighters penetrated deep into Herat city, and there were heavy clashes with Afghan security forces near the UNAMA provincial headquarters, officials said.

It also came as US-led foreign forces near a complete withdrawal of troops and Afghan security forces struggle to hold back Taliban fighters in three major provincial capitals. In a statement following the attack, the UN said it was urgently seeking to establish a full picture of the assault and was in contact with the relevant parties.

It was not immediately clear who attacked the compound, but a western security official told Reuters all diplomatic compounds in the city were put on high alert.

“The US strongly condemns the attack on the UN compound in Herat,” White House national security adviser Jake Sullivan said in a statement, reiterating a US call for reduction in violence in Afghanistan.

UNAMA said the attack was against the entrances of the compound that were clearly marked as a UN facility.

“This attack against the UN is deplorable and we condemn it in the strongest terms,” said Deborah Lyons, the UN secretary-general’s Special Representative for Afghanistan.

UNAMA said no UN personnel were hurt.

The Taliban put the incident down to possible crossfire. “It is possible that guards could have sustained harm in crossfire due to close proximity of the office to the fighting,” the insurgents’ spokesman, Zabihullah Mujahid, said on Twitter.

He added that Taliban fighters had“ arrived at the scene” and that the compound was “not under any threat”.

The Taliban have already captured swathes of the province of Herat.