Zara, the fashion retailer, was forced to apologise to ultra-Orthodox Jews after its Israeli stores sold a men's suit with a mix of materials that are considered non-kosher to some strict religious Jews. The Spanish clothing empire took out a series of adverts in Israeli newspapers to apologise for the error, which it said happened after a mistake in one of its factories. The suit contained a combination of cotton and linen which some rabbinical authorities class as an "unnatural" blend, known as shatnez to ultra-Orthodox Jews.

In a statement, the company said: "Zara regrets this mistake and would like to reassure its clients in Israel and particularly Orthodox Jews that it will do everything possible to prevent it happening again." Zara has also promised to refund the cost of scientific checks for shatnez, which Orthodox Jews routinely carry out when they buy clothes. They return those which test positive.

The ban on shatnez materials is mentioned in the Torah in the books of Leviticus and Deuteronomy. It prohibits the combining of various fabrics in one garment, the interbreeding of different species of animals and the planting together of different types of seeds. Zara, which is the flagship of the Inditex brand, opened stores in Israel 10 years ago. It is now the country's largest clothing company, with 15 stores, 900 employees and annual sales of £172m.