BERLIN (Reuters) - Border controls introduced by Germany could be extended beyond Dec. 15 if necessary as they have proved very successful in fighting smugglers and irregular migration, the German interior minister said.

"For me, the border controls will remain as long as necessary," Nancy Faeser said on Tuesday in the city of Goerlitz on the Polish border, adding that this would probably be until the European asylum system takes effect.

The European Union agreed in December on new rules to handle irregular arrivals of asylum seekers and migrants, a deal hailed as a breakthrough after almost a decade of bitter feuds on the issue. It could take until the end of 2025 for the pact to take full effect.

Germany announced stricter controls on its land borders with Poland, the Czech Republic and Switzerland in response to a sharp increase in first-time asylum requests last year.

"We have achieved great success in reducing irregular migration, the fight against smugglers has been very effective," the minister said.

Berlin will have to notify the European Commission of an extension, Faeser said.

(Reporting by Kirsti Knolle; Editing by Madeline Chambers)