Barack Obama on Tuesday flashed a hint of steel in the increasingly urgent debate over healthcare reform, warning private insurers they would face tough new regulations and saying their opposition to a public insurance plan “defies logic”.

But the US president, who says healthcare reform is his overriding domestic priority, said he had yet to draw “any lines in the sand” in terms of what he would consider a minimally acceptable reform package from Congress. In a rare display of sarcasm, he said he took “advocates of the free market to heart” when they claimed private insurers could provide the best healthcare and service to families.