WASHINGTON (Reuters) - The United States said on Friday it was "deeply troubled" that Iranian courts had upheld a 16-year prison term against journalist and human rights activist Narges Mohammadi, and it urged Tehran to release her on humanitarian grounds.

"No one should be jailed for peaceful, civic activism," State Department spokesman Mark Toner told a news briefing, noting reports indicated Mohammadi's health was "rapidly deteriorating while in prison" and she had been barred from communicating with her two young children.

"Given these circumstances, the imposition of this prison sentence is particularly harsh and unjustified and we call on the government of Iran to provide Mohammadi with adequate medical care and to release her on humanitarian grounds," Toner said.

Mohammadi was arrested last year after launching a campaign to end the death penalty in Iran. She was sentenced to 16 years in prison in May for founding the anti-death penalty movement, which was deemed to be an illegal splinter group.

Mohammadi, a vice chair of the Center for Supporters of Human Rights, had previously been sentenced to five years in prison for conspiring against the Islamic Republic and one year for anti-government propaganda due to her human rights activism.

She had been released on bail for medical reasons but was rearrested last year and ordered to serve out the earlier sentences because of her work campaigning against the death penalty.

(Reporting by David Alexander; Editing by Sandra Maler)