The announcement on Wednesday comes ahead of National Assembly elections scheduled for September and marks the beginning of a major Nato expansion outside the Afghan capital.
Several hundred Italian soldiers are expected to staff the base in Herat, while in Farah - to the south, US troops will come under ISAF command. Both provinces are on the Iranian border.
"It is ... ISAF's first critical step into the western region of Afghanistan, which will allow ISAF to more effectively support the upcoming ... elections," said Lieutenant General Ethem Erdagi, the ISAF commander.
Force officials added that by the end of the summer, two additional military bases in western Afghanistan will be operational - one in Chagcharan, capital of Ghor province, and a second in Qaleh, capital of Baghdis province.
Lithuanian and Spanish troops will be deployed in these bases respectively.
The ISAF is a peace-keeping force that numbers about 8000 soldiers from 47 countries. Nato took command of the ISAF in 2003, its first mission outside its Europe-Atlantic area of operation.
Nato Secretary-General Jaap De Hoop Scheffer said on Tuesday that the alliance was determined to stay in Afghanistan despite growing violence against its forces.
"Nato is committed to Afghanistan," Scheffer said. "We hope, of course, that it will be possible to prevent further violence."
Nato chief Jaap de Hoop Scheffer
(C) plans to expand operations
Britain takes command of the ISAF in 2006, and there have been reports of plans for British troops to take over two military bases in the south, but no announcement has been made. A British embassy official declined to comment.
The US leads a separate international force of 18,300 - most of them Americans – who are searching for Usama bin Laden, as well as for Taliban fighters, mainly in the country's south and east.
The Taliban claimed responsibility on Monday for a bicycle bomb aimed at an ISAF vehicle, which wounded at least seven Afghans, and a rocket, which slammed into the force's base in Kabul.
The twin blasts highlighted deteriorating security in Kabul since the ousted government launched a renewed offensive in recent months.
Interior Ministry spokesman Lutfullah Mashal confirmed that the blast in the Hod Qhail region, east of Kabul, targeted an ISAF vehicle. "It was aimed at an ISAF vehicle, but missed it and struck a taxi and pedestrians passing by."
A spokesman for the Taliban opposition, Abdul Latif Hakimi, claimed responsibility for both attacks.
"We are sorry for the civilian losses, but they were driving too close to ISAF vehicle and we advise them to keep their distance from foreign troops for their own safety," said Hakimi.
Hakimi also claimed that an ISAF vehicle was destroyed in the bicycle bomb blast, but that was not confirmed by the authorities.
The Taliban, ousted by a US-led military operation in late 2001 for failing to hand over bin Laden after 9/11, have stepped up its campaign against foreign forces since the end of the winter.