By Syed Raza Hassan
KARACHI, Pakistan (Reuters) - A lone gunman on a motorbike shot dead a senior Pakistani police officer in the volatile southern city Karachi on Friday, police said, the third in an sudden spate of killings targeting senior officers in the city.
"The killing of three senior ranking officers in 15 days is quite unusual," a senior police officer requesting not be named told Reuters.
"Earlier, low-ranking policemen like constables and assistant sub-inspectors were being targeted, but now the pattern is changing."
It was unclear who was behind the shootings, or even if they are linked. Friday's killing of Superintendent Ejaz Haider was claimed by both a Taliban spokesman and a Twitter account purporting to be from a breakaway group of Pakistani militants who have sworn allegiance to Islamic State, according to the SITE Intelligence Group, which monitors jihadi communications. Neither claim could be immediately verified. Pakistani authorities doubt that Islamic State has operational links with Pakistani militants.
But it underline fears that the ultra-violent Islamic State is inspiring Pakistani militant groups to emulate it, even if the groups do not share funding or fighters.
The shooting of Haider, who was a minority Shi'ite, follows Wednesday's massacre of 45 Shi'ite Muslim commuters in Karachi. That attack was also claimed by militants who swore allegiance to Islamic State.
Leaflets left at the scene denounced Shi'ites and hailed Islamic State, but also denounced extrajudicial police executions and named one officer accused of involvement in a number of killings.
Police publicly deny killing suspects but privately many say the country's broken judicial system means they must either kill militant suspects or see them walk free.
Pakistan is facing growing sectarian violence; around a fifth of its 180 million citizens are Shi'ites.
But other police said Haider's shooting might be motivated by a personal grudge.
So far 48 policemen have been killed in Karachi this year, compared to 142 last year.
(Reporting by Syed Raza Hassan; Editing by Katharine Houreld)