The corruption scandal around an economic-development fund in Malaysia is spilling beyond the country’s borders, as officials at a United Arab Emirates state investment vehicle raise questions about more than a billion dollars in money that they said is missing.

Abu Dhabi has long been a source of support for the fund, 1Malaysia Development Bhd., which was set up six years ago by Malaysian Prime Minister Najib Razak to develop new industries in the Southeast Asian country. Now, as 1MDB tries to fend off a cash crunch, its...