"If the deputy chairperson is able to regret it in English, I assume that the party leader Siv Jensen can regret it in Norwegian," Stoltenberg said on Tuesday after the Progress Party briefed international press on its policies.
Ketil Solvik-Olsen, the party's deputy leader, yesterday told a meeting with foreign journalists that Jensen's claim that Norway faced the threat of "sneak-islamization" had been unfortunate.
But Jensen on Tuesday evening stood by her provocative past statements.
"I'm not going to apologize for that and I and the Progress Party will continue to fight the emergence of such radical forces and the ideas they advocate," she wrote in an email to VG newspaper.
In February 2009, Jensen said: "The truth is that we are beginning to allow a form of sneak-Islamization to take place in this country."
She said on Tuesday that she remained concerned by radial Islamic groups.
"I am concerned that we have radical groups in Norway who want Shariah law and an entirely different way of organizing society in Norway. No one should be in any doubt that this is an important issue for us," she said.
Meanwhile, a survey of Progress party politicians conducted by the Dagbladet newspaper showed that 61 percent saw immigration as the most important issue in the ongoing coalition negotiations.
This compares with just 16.6 percent who saw lower taxes as the the most important issue, belying Solvik-Olsen's depiction of the party on Tuesday as driven primarily by desire for lower taxes and less regulation.