U.S. Republican presidential nominee Donald Trump insisted on Monday he was not changing his stance on immigration, despite a comment from a top aide who said his plan to deport 11 million illegal immigrants was still under review.

¡°I¡¯m not flip-flopping. We want to come up with a really fair but firm answer,¡± Trump told Fox News. He did not elaborate on his policy.

On Sunday, Kellyanne Conway, Trump¡¯s campaign manager, was pressed repeatedly in a CNN interview on whether Trump would go ahead with a call he made in November to set up a ¡°deportation force¡± to remove undocumented immigrants.

¡°To be determined,¡± Conway said. She also said Trump was committed to a ¡°fair and humane¡± approach to those living in the country illegally.

Trump¡¯s immigration position has been a centerpiece of his campaign. When he announced he was running for president, he called for construction of a wall along the nation¡¯s border with Mexico to stop undocumented immigrants from entering the country. He has insisted that he will make Mexico pay for the wall.

Trump also said that Mexico was sending ¡°rapists¡± and ¡°criminals¡± across the border.