Vodafone Group PLC intends to work with an Iranian internet-service provider to help improve its local networks, becoming the first big Western firm to jump into Iran after the U.S. moved earlier this month to make it easier for companies to do business in the Islamic Republic.

The U.Khttp://www.wsj.com/articles/obama-administration-further-eases-financial-sanctions-on-iran-1475942805. telecommunications carrier said Tuesday that it plans to assist Iran’s HiWEB, a small, privately owned operator, in modernizing infrastructure...