DOHA (AFP) - A death sentence handed to a Filipino in Qatar for spying was reduced on appeal by a Doha court on Sunday to life imprisonment.

Two other sentences of life imprisonment against another pair of defendants, also from the Philippines, were reduced at the same time by Qatar's Court of Appeal to 15 years' jail.

One of the men sentenced to serve 15 years has been named as Ronaldo Lopez Ulep. All three had been convicted last year on charges of espionage and passing on Qatar military and economic secrets to the Philippines government.

The unnamed defendant who was originally sentenced to death is likely to spend up to 25 years in prison. He worked as a supervisor at Qatar Petroleum.

The other two defendants worked for the Qatar Air Force.

At the time of their conviction it was alleged that the two men working for the air force supplied information to the third man for cash.

Following Sunday's brief hearing, the Philippines ambassador to Qatar, Mr Wilfred C. Santos, said the reduction in sentences was "welcome" but a further appeal may take place.

"We welcome this development and we will continue to monitor the case," he said.

"We are willing to exhaust all legal avenues."

Manila has "emphatically" denied spying on Qatar.

All three men have been detained since 2010.

The case has raised concerns among rights groups, which question the convictions and allege the three men have been tortured while being detained.

Amnesty International alleges Lopez Ulep spent four years in solitary confinement and was convicted "on the basis of a 'confession' he was forced to sign, even though it was written in Arabic and he could not read it".

Ahead of Sunday's hearing, Amnesty released a blog from the 17-year-old daughter of Lopez Ulep, who said her father was dragged away from their Doha home in April 2010 and the family have not seen him since.

She said investigators took laptops, photos and the family's savings hidden in a safe.

The teenager, who is now in the Philippines, urged the Qatari authorities to release her father and "return what they took from us for the past five years".

Mr Santos said Manila knew about the allegations of torture.

"We are aware of these and are taking note of this," he said.

Relatives of the defendants were also at court but refused to comment afterwards.