At least 63 people have been killed in a suicide bomb attack during a rehearsal for a military parade in the Yemeni capital, Sanaa, officials say.

The assailant, who was reportedly wearing army uniform, blew himself up among a group of soldiers at al-Sabin Square, near the presidential palace.

An al-Qaeda source told the BBC one of its members had carried out the attack.

It was the deadliest incident in the capital since President Abdrabbuh Mansour Hadi took power in February.

"We were in a parade, suddenly there was a huge explosion. Dozens of our men were killed. We tried to help them," Col Amin al-Alghabati told the Reuters news agency.

"The suicide bomber was dressed in a military uniform. He had a belt of explosives underneath," he added.

Recently there have been daily casualties in fighting in the mountainous southern desert and towns between government forces, backed by US military advisers, and militants linked to al-Qaeda.

But Sanaa has been relatively quiet since the longstanding President Ali Abdullah Saleh stepped down reluctantly.

So this is a message, almost certainly from al-Qaeda, to the new President, Abdrabbuh Mansour Hadi, that he can expect no let-up in the fight between the army and the militants.

Coupled with the attack on US advisers to Yemen's coast guard it will be a worrying development for Washington and the West, since Yemen is home to al-Qaeda's most dangerous branch, responsible for building and sending a succession of sophisticated bombs onto planes bound for the US.