HANOI (Reuters) - Financial institutions are not at risk from the first cyberattack on a Vietnamese brokerage, the market regulator said on Wednesday, after the third largest securities firm was suspended after it was targeted over the weekend.

VNDirect, Vietnam's third largest broker in terms of transactions handled according to the Ho Chi Minh City exchange, has been disconnected from the trading system since Monday.

"We do not see risk of contagion," Pham Hong Son, the vice chairman of Vietnam's State Securities Commission (SSC), told Reuters, adding that no other brokers had been affected.

VNDirect was still disconnected from the system on Wednesday as of 0600 GMT. It declined to comment on when it would resume trading. It also declined to say how much damage it had sustained in the attack.

In a note published on Monday, the broker said its "entire system was attacked by an international organization" on Sunday, making its trading platform temporarily inaccessible, but with no impact on customers' assets or data. The company's shares have fallen by nearly 4% since the start of the week.

Asked about the attacker, the SSC declined to comment.