* Riot began after police raid
* Journalist and author Lyra McKee killed
* Police say New IRA group likely to blame (Adds reaction from Irish, UK PMs, U.S. Pelosi)
By Amanda Ferguson
BELFAST, April 19 (Reuters) - An off-duty journalist was killed after shots were fired during rioting in the Northern Irish city of Londonderry overnight, an attack that shocked the province and police said was likely the work of nationalist militants.
Rioting erupted in the Irish nationalist Creggan area of the city late on Thursday following a raid by police, who said they were trying to prevent militant attacks over the weekend. At least 50 petrol bombs were thrown and two cars set on fire.
"Unfortunately at 11 o'clock last night a gunman appeared and fired a number of shots towards the police and a young woman, Lyra McKee, 29 years old, was wounded" and later died, Police Service of Northern Ireland Assistant Chief Constable Mark Hamilton told journalists on Friday.
McKee, a journalist whose work has been published in magazines and newspapers both in Northern Ireland and abroad, was writing a book on the disappearance of young people during the three decades of sectarian violence in Northern Ireland, which ended with the 1998 Good Friday Agreement peace deal.
"The death of Lyra McKee in last night's suspected terrorist incident in Londonderry is shocking and truly senseless," British Prime Minister Theresa May said in a statement.
Described by her publisher Faber as a rising star of investigative journalism, McKee's death was condemned by both Irish nationalist and pro-British unionist politicians.
"We are all full of sadness after last night's events. We cannot allow those who want to propagate violence, fear and hate to drag us back to the past," Irish Prime Minister Leo Varadkar said in a statement.
Police said they were treating the incident as a terrorist attack and had opened a murder inquiry. The New IRA group, which has been responsible for several attacks in recent years, was most likely behind the killing , Assistant Chief Constable Hamilton said.
Saoradh, a political party with links to dissident militants, said in a statement it understood McKee was standing close to police and was killed accidentally by a "Republican Volunteer."
Police said they did not believe she was working at the time of the attack.
"NO ONE WANTS TO GO BACK"
U.S. House of Representatives Speaker Nancy Pelosi, who led a congressional delegation to Londonderry earlier on Thursday, told a news conference that McKee's death was a tragedy that was in sharp contrast to the peace created by the Good Friday Agreement which Washington helped broker 21 years ago.
The detonation of a large car bomb outside a courthouse in Londonderry in January highlighted the threat still posed by militant groups opposed to the Good Friday Agreement.
The groups, which are far smaller than those that operated before the peace deal and have very limited public support, have previously launched attacks during the Easter period.
Politicians in Northern Ireland have warned that Britain's plans to leave the European Union could undermine the peace deal and that any border infrastructure would become targets for militant groups.
"Those who brought guns onto our streets in the 70s, 80s & 90s were wrong," Democratic Unionist Party (DUP) leader Arlene Foster said on Twitter. "It is equally wrong in 2019. No one wants to go back."
A local journalist at the scene of Thursday's shooting, Leona O'Neill, wrote on Twitter that after McKee was hit and fell beside a police Land Rover, officers rushed her to hospital, where she died.
Videos posted on social media showed police vehicles being pelted with what she said were dozens of petrol bombs, bricks, bottles and fireworks.
(Additional reporting by Conor Humphries and Padraic Halpin in Dublin; Editing by Peter Cooney and Kirsten Donovan)
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