The employees were travelling by road on Friday when they were stopped by a local armed group, said Marek Resich, a spokesman for the International Committee of the Red Cross (ICRC).
“The ICRC is currently in contact at various levels to secure the safe release of its team,” he told the Associated Press.
The Red Cross workers were delivering sheep to local villages when they were surrounded by gunmen, said Raouf Ahamadi, a police spokesman in Herat province.
Recently, attacks have also been aimed at civilian aid workers. On 24 July, armed locals fired on two Finnish aid workers in Herat, killing both of them.
Herat borders Iran in the west and is a centre of trade with Iran and central Asia.
The Police Chief in Herat province said on August 3 that the Iranian regime was partly behind the recent wave of attacks in the province.
General Samiullah Qatrah, said that at least six people who have been involved in coordinated attacks were arrested over ten days. They have confessed to the killings of 11 people, including two Finish nationals, he said.
General Samiullah Qatrah said several Taliban commanders who played roles in recent attacks in Herat and are provided significant levels of financial support by the Iranian regime are able to freely enter Iran and return to Afghanistan unimpeded.
“In their confessions, they have said that the network is funded by Iran,” General Qatrah asserted.
In recent months insecurity has increased around Afghanistan.
Based on statistics provided by Herat Provincial Council, over the past four months, more than 80 people have been killed in the province by unknown armed men.