The all-monks party of the JHU, or National Heritage Party, and the Marxists said on Thursday they opposed Norway's continued participation in the faltering peace process aimed at ending the conflict between Tiger rebels from Sri Lanka's Tamil minority and the Sinhalese majority.
They accuse Norway of siding with the Tigers.
"We told the president even at the beginning of this week we were against Norway," JHU spokesman Champika Ranawaka said. "But we will not make it an issue to withdraw our support to the president."
The Marxist JVP, or People's Liberation Front, too, opposed Oslo's involvement but would not withdraw crucial support for the president, a party spokesman said.
"Norway's behavior is not reasonable," JVP spokesman Wimal Weerawansa said.
"There's no change in our stance, but that does not mean that the president cannot take a decision going against our party policy."
President Mahinda Rajapakse's invitation on Wednesday to Norway followed a surge in violence blamed on Tamil Tiger rebels that has claimed 29 lives, including 17 soldiers in a weekend blast.
The violence has heightened fears that the country can slide back into ethnic civil war.