MUNICH (Reuters) - Bavarian state premier Horst Seehofer has invited U.S. President-elect Donald Trump to visit the southern German state, possibly as soon as February for the Munich Security Conference, a source familiar with the invitation said.

Seehofer, who heads the Christian Social Union (CSU), sister party to Chancellor Angela Merkel's conservative Christian Democrats (CDU), extended the invitation in a letter of congratulations to Trump after his victory, said the source.

The Feb. 17-19 conference, a forum for debate about international security, often draws senior officials from around the world.

Trump will be inaugurated on Jan. 20.

It was not immediately clear when a sitting U.S. president last participated in the event, and the security conference organizers could not immediately be reached for comment.

Seehofer's CSU and Merkel's CDU, which form a bloc in the German parliament, have been at odds over Merkel's migrant policy, which saw nearly 900,000 people enter Germany last year, an issue likely to play a major role in elections in September.

During the U.S. election campaign Trump called Merkel's refugee policy a "disaster" that had boosted crime rates.

Statistics compiled by the German Interior Ministry showed the number of crimes reported in 2015 - excluding visa and other immigration violations - remained essentially unchanged from the previous year at 5.9 million.

Seehofer told the Augsburger Allgemeine newspaper in an interview published on Thursday that his party would only participate in a coalition government in 2017 that agreed to its demand for an upper limit on migration.

Merkel, who on Sunday announced her decision to run for a fourth term, has rejected setting an upper limit for migration.

(Reporting by Joern Poltz in Munich and Andrea Shalal in Berlin; Editing by Janet Lawrence)