Image copyright CBS Image caption The boy cannot survive for much longer, and must urgently see his mother, the family say

The Yemeni mother of a dying boy in California is being prevented from seeing him due to a US ban on visitors from her country, the family says.

Two-year-old Abdullah Hassan was born with a brain disease that doctors say he will not survive.

His relatives say his mother wants to see him one last time before they take him off life-support.

His father says the boy's mother cannot come to the US due to the Trump administration's travel ban.

Though Abdullah and his father were born in Yemen, they are American, says the family.

"All she wishes is to hold his hand for the last time," the boy's father, Ali Hassan, 22, told the San Francisco Chronicle on Sunday.

He said the boy would probably die if he is taken to Egypt, where his mother is currently living.

Mr Hassan's wife, Shaima Swileh, is currently seeking a waiver from the US Department of State to travel to the US urgently.

Image copyright CBS

What is the US travel ban?

Soon after he took office, US President Donald Trump imposed travel restrictions on mainly majority Muslim countries.

The executive order went through several versions before being upheld by the US Supreme Court this summer.

It bans nationals of Iran, North Korea, Venezuela, Libya, Somalia, Syria and Yemen from entering the US.

Media playback is unsupported on your device Media caption Muslim students on Trump ban: 'I don't belong here'

'Unfathomably cruel'

Saad Sweilem, from the Council on American-Islamic Relations, which is advocating for the family to be reunited, said barring Abdullah's mother was "unfathomably cruel."

Mr Hassan's family came to California in the early 1980s, but maintained close ties with their native Yemen.

His son Abdullah was diagnosed with hypomyelination, a brain disease that has affected his ability to breathe.

When he was eight months old, the family moved from Yemen to Cairo to escape that country's civil war.

About three months ago, Mr Hassan brought his son to the US for treatment, with the expectation that his wife would later join them.

But after doctors in Oakland, California, informed him that the boy's condition was terminal, the family applied for her to travel to the US.

They say they received a rejection letter from the state department, citing the US president's travel ban.

A state department official who did not wish to be named refused to discuss the specific case due to confidentiality laws.

But the official told the BBC they make "every effort to facilitate legitimate travel by international visitors".

"We are also fully committed to administering US immigration law and ensuring the integrity and security of our country's borders."