March 12 (Reuters) - Medical device maker Stryker said on Thursday a cyberattack that hit its computer systems a day earlier is causing widespread disruption to its business, including its ability to process orders, make products and ship them to customers.

An Iranian-linked hacking group called Handala claimed responsibility for the attack, saying it was in retaliation to a strike on a girls' school in Minab, southern Iran.

The school was hit on the first day of U.S.-Israeli attacks on Iran, killing an estimated 150 students, according to Iran's ambassador to the U.N. in Geneva, Ali Bahreini. Reuters has not independently verified the figure.

Stryker first disclosed the issue on March 11, saying it had experienced a global disruption to its Microsoft ( MSFT ) environment.

The incident has not affected any patient-related services and its connected medical products, the company said, even though the full scale and financial impact are not yet known.

The company, which has 56,000 employees and operations in 61 countries, said its investigation is ongoing.

(Reporting by Kamal Choudhury in Bengaluru; Editing by Arun Koyyur)