BERLIN (Reuters) - Thirteen regional lawmakers from the anti-immigrant Alternative for Germany (AfD) quit on Tuesday over what they called the anti-Semitic views of a colleague, causing a damaging split in the right-wing party.

The AfD has won growing popular support in Germany due in part to Europe's migrant crisis, which has seen more than 1 million refugees arrive in the country over the past year, and it now has seats in eight of Germany's 16 state assemblies.

However, Wolfgang Gedeon, a former doctor turned AfD lawmaker in the southern state of Baden-Wuerttemberg, has triggered outrage by saying that denial of the Nazi Holocaust, in which six million Jews were killed, is a legitimate expression of opinion. Holocaust denial is a crime in Germany.

Joerg Meuthen, the leader of the AfD parliamentary group in Baden-Wuerttemberg and the party's co-chair at the national level, led Tuesday's split. He and 12 others left the regional parliamentary group, which originally comprised 23 lawmakers.

"Anti-Semitism cannot and must not have any place in the AfD," Meuthen said.

The AfD parliamentary group had previously rejected an attempt by Meuthen for Gedeon to be expelled from the party. Instead, they suspended his membership pending an independent review of his written work.

The national leaders of the AfD said in a statement that there was no room for anti-Semitism in the party and criticized those in the state who resisted Gedeon's expulsion.

"The board distances itself from those members who do not leave the parliamentary group with Joerg Meuthen. From now on we recognize only Joerg Meuthen and the lawmakers who join him as representatives of the AfD in the Baden-Wuerttemberg assembly," said the board in a statement.

An INSA poll published on Tuesday put nationwide support for the AfD at 14.5 percent, up 0.5 percentage points from the previous survey. Chancellor Angela Merkel's conservative bloc were on 30 percent and her center-left coalition partners, the Social Democrats, on 21 percent.

Germany holds a parliamentary election next year.

In May, AfD Vice Chair Alexander 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; Writing by Madeline Chambers and Paul Carrel; Editing by Gareth Jones)