BERLIN (Reuters) - A regional branch of the anti-immigrant Alternative for Germany (AfD) split in two on Wednesday as a war of words erupted over the party's handling of an anti-Semitism row with one senior member sharply criticizing national co-leader Frauke Petry.

The AfD has won growing popular support in Germany due in part to Europe's migrant crisis, which has seen more than a million refugees arrive in the country over the past year. It now has seats in eight of Germany's 16 state assemblies.

However, the party encompasses a wide range of views which has led to a degree of internal strife. Wolfgang Gedeon, a doctor turned AfD lawmaker in the southern state of Baden-Wuerttemberg, caused outrage last month for his view that Holocaust denial was a legitimate expression of opinion.

Denial of the Nazi Holocaust, in which six million Jews were killed, is a crime in Germany.

A row ensued with the head of the AfD group in the state assembly, Joerg Meuthen, failing to win enough support for Gedeon to be expelled.

The crisis came to a head on Tuesday when 13 lawmakers, led by Meuthen, quit the parliamentary party in the state and national leader Frauke Petry rushed to Stuttgart. That led to Gedeon's resignation.

On Wednesday, the AfD parliamentary group -- originally numbering 23 -- officially split into two. Meuthen, widely seen as a moderate within the AfD, leads one group and Petry has said she backs the remaining members, minus Gedeon.

Petry's involvement has incensed some in the party who do not wholeheartedly support her.

In comments widely seen to undermine Petry, AfD Vice Chair on a national level, Alexander Gauland, launched a broadside against her, saying her dash to the state had merely helped escalate the crisis.

"I would never have thought of becoming politically active in (the state of) Saxony without Frauke Petry if there were difficulties there," he told Reuters Television. Petry is head of the AfD in the eastern state of Saxony.

A Forsa poll on Wednesday put nationwide support for the AfD at 9 percent, down 1 percentage point from the previous survey. Germany holds a federal parliamentary election next year.

In May, Gauland caused a storm by saying Germans would not want to live next door to national soccer star Jerome Boateng, born in Berlin to a Ghanaian father.

(Reporting by Hans-Edzard Busemann, Andreas Rinke and Reuters TV; Writing by Madeline Chambers and Caroline Copley; Editing by Richard Balmforth)