Azerbaijan on Tuesday sentenced award-winning investigative journalist and anti-graft campaigner Khadija Ismayilova to seven and a half years in jail on corruption charges she denounced as trumped-up, her lawyer said.

Considered Azerbaijan's most prominent critical journalist, Ismayilova, 39, served as bureau chief for the local service of the US-funded Radio Free Europe/Radio Liberty network between 2008 and 2010.

"Baku's Court for Serious Crimes sentenced Khadija Ismayilova to seven and a half years in prison for economic crimes, including illegal entrepreneurship and tax evasion," her lawyer Fariz Namazly told AFP.

"We will appeal the illegal verdict," he added.

Held in pre-trial detention since December, Ismayilova had denounced her prosecution as politically motivated and an attempt to stop her critical reporting.

The journalist has fearlessly probed the alleged vast riches amassed by President Ilham Aliyev and his family.

In her final statement to the court on Monday, Ismayilova vowed the authorities "won't be able to force me to stay silent, even if they sentence me to 15 or 25 years."

Ismayilova's mother Elmira Ismayilova, who was present in the courtroom on Tuesday, told AFP: "Khadija said she is strong enough to bear everything as she fights for a right cause."

Human Rights Watch said: "The outrageous verdict against Khadija Ismayilova shows the Azerbaijani authorities' willingness to subvert the law to exact revenge against critics."

"Her conviction and sentence should be immediately set aside," the group's executive director Kenneth Roth, said in a statement.

Denis Krivosheev of Amnesty International rights watchdog was equally scathing, saying it was "yet another unfair trial relying on fabricated charges."

"Ismayilova's only crime was to investigate high-level government corruption with courage and persistence," said Johann Bihr, the head of Eastern Europe and Central Asia desk at the Reporters Without Borders media advocacy group.

- 'Enemy of the government' -

In a leaked diplomatic cable from 2009 published by Wikileaks, Aliyev is said to have described Ismayilova as an "enemy of the government", asking the US ambassador to Azerbaijan to intervene to have her sacked by Radio Liberty.

In December, Azerbaijani police raided and closed the Baku offices of Radio Liberty in a move that Washington called deeply disturbing, aggravating concerns about the treatment of non-state media in the Caucasus nation.

In 2012 Ismayilova said she was the victim of blackmail, after a covertly-filmed video with sex scenes purportedly involving her was posted on the Internet.

Rights groups said the footage was released by supporters of Aliyev in retaliation for Ismayilova's work exposing his daughters' alleged business interests.

Rights groups accuse the government of Azerbaijan of stepping up pressure on opponents after Aliyev's reelection to a third term in 2013.

Earlier this month, Azerbaijan jailed a prominent rights activist couple to lengthy jail terms in a case that was also decried as politically motivated.

The high-profile trials kicked off after Azerbaijan in June hosted with great fanfare the inaugural edition of the European Games, a sporting extravaganza billed as Europe's answer to the Olympics.

In the same month, U2 singer and political activist Bono spoke out in support of six jailed Azerbaijani activists including Ismayilova and Yunus from the stage at concerts in Canada.

Freedom House says there are now more than 80 political prisoners in Azerbaijan.

Aliyev, 53, strongly denies accusations of rights abuses, while his administration has dismissed such criticism as a smear campaign.

Aliyev took over after the death of his father Heydar Aliyev, a former KGB officer and communist-era leader who had ruled newly independent Azerbaijan with an iron fist since 1993.