SAN FRANCISCO, July 15 (Reuters) - Multiple high-profile Twitter (TWTR.N) accounts were hijacked on Wednesday, with some of the platform’s top voices - including U.S. presidential candidate Joe Biden, reality TV star Kim Kardashian, former U.S. President Barack Obama and billionaire Elon Musk, among many others - used to solicit digital currency.

Hours after the first wave of hacks, the cause of the breach had not yet been made public. In a sign of the seriousness of the problem, Twitter took the extraordinary step of preventing at least some verified accounts from publishing messages altogether.

It was not clear whether all verified users were affected but, if they were, it would have a huge impact on the platform and its users. Verified users include celebrities, journalists, and news agencies as well as governments, politicians, heads of state and emergency services.

Most of those users had their ability to tweet restored hours later, Twitter said in a statement, although it cautioned account functionality “may come and go” as it continued to work on a solution.

Chief Executive Jack Dorsey said the company was diagnosing the problem and pledged to share “everything we can when we have a more complete understanding of exactly what happened.”

“Tough day for us at Twitter. We all feel terrible this happened,” he said in a tweet.

The unusual scope of the problem suggests hackers may have gained access at the system level, rather than through individual accounts. While account compromises are not rare, experts were surprised at the sheer scale and coordination of Wednesday’s incident.

“This appears to be the worst hack of a major social media platform yet,” said Dmitri Alperovitch, who co-founded cybersecurity company CrowdStrike.

Congressman Frank Pallone, the chairman of the House energy and commerce committee, called on the company to account for what went wrong.

“Twitter needs to explain how all of these prominent accounts were hacked,” he said in a tweet.