The head of the anti-migrant Alternative for Germany (AfD) party, Frauke Petry, told local media on Saturday that border security officials should use their guns to fire at migrants who try to enter the country illegally.
"We need comprehensive controls so that there are no longer so many unregistered migrants entering via Austria," Petry told the newspaper Mannheimer Morgen.
Police officers must prevent illegal immigration, "making use of their guns as a last resort. Just as the law says."
Petry's comments have attracted criticism from the centre-left and pro-migrant parties.
Nonetheless, her party's increasingly radical stance on the migrant crisis has proven popular among many voters dismayed by Germany's chaotic handling of the huge influx in arrivals, which saw 1.1 million asylum seekers enter Germany last year.
Last week, AfD became the third-strongest party in the country in opinion polls following the parties in Merkel's ruling coalition.
Petry was echoing comments made by her partner and fellow AfD member Marcus Pretzell, who had already called in November for the use of firearms to fend off migrants who refuse to adhere to border laws.
At a regional party conference on Saturday, Merkel said she expected that many refugees and migrants currently living in Germany would at some point return to their home countries.
"We expect that - once peace returns to Syria, once Islamic State has been defeated in Iraq - they will head back to their home countries with the knowledge that they have gained here," Merkel told party delegates in the north-east town of Neubrandenburg.
Merkel's coalition agreed to tighten asylum laws late Friday, as public pressure grows on the chancellor to get a better grip on the number of arrivals in the country.
Critics say Merkel's attempts to stem the inflow of migrants is too little too late, and 200 AfD supporters protested against the government's refugee policy at Saturday's conference.