Igor Plotnitsky, the head of the self-proclaimed Lugansk People's Republic, "was wounded this morning as a result of a powerful explosion that occurred near his car," the official pro-Russian rebels' news agency said.
Plotnitsky, 52, is being treated at a local hospital along with several other people who suffered injuries in the blast in Lugansk city, the report said.
The rebels' news agency claimed the explosion was an "attempt on the life" of their leader but did not point the finger of blame at any individual or group.
Plotnitsky, the former commander of a pro-Russian rebel group, was elected in November 2014 to head the Lugansk region in polls denounced by Kiev as a breach of a ceasefire agreement.
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Lugansk is the smaller of two breakaway pro-Russian provinces that has been fighting Ukrainian government forces for more than two years.
A suspected car bombing in the Lugansk region in December killed pro-Russian leader Pavel Dremov in what rebels said was a "terrorist act organised by the Ukranian security forces."
In May 2015 Lugansk rebel commander Alexei Mozgovoi was killed in an attack against his vehicle.
Kiev and the West have accused Russia of supporting rebels and deploying troops across the border, claims that Moscow vehemently denies.