"Hillary Clinton wants to be America's Angela Merkel and you know what a disaster this massive immigration has been to Germany," he told a crowd.

"My opponent wants to increase, which is unbelievable no matter who you are and where you come from, the flow of Syrian refugees by 550 percent," he said.

Republican Senator Jeff Sessions, a senior policy adviser to Trump, described Trump's strategy as "foreign policy realism," while Democratic Senate Minority Leader Harry Reid said Trump should take a US naturalization test himself as he prepares to propose new political hurdles for immigrants coming to the country.

"Since Donald Trump wants to impose new tests on immigrants, he should take the one test every immigrant has to pass to become a United States citizen," Reid said in a statement. "He would almost certainly fail, given his general ignorance and weak grasp of basic facts about American history, principles and functioning of our government."

Despite increasing criticism on his national security remarks from the Democrats and many Republicans including 50 senior former national security experts who issued an open letter last week saying he was too reckless to be president, Trump went on with a more nuanced tack in his Monday speech, local analysts observed.