Left MPs, who met the Prime Minister, said Singh told them that Italy's decision was "unacceptable".
However, PMO sources said Singh only told the delegations that the matter would be looked into and he will ask External Affairs Minister Salman Khurshid to take up the issue with Italy.
Delegations of angry Left and Congress-led UDF MPs met Singh separately to express anguish and demand his intervention in the "serious" matter.
"He (PM) said this is unacceptable to us," Rajesh added.
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Another party MP P Karunakaran told a press conference separately that Singh "told us that this is not acceptable to us" and assured the delegation that the matter would be taken up "strongly" with the Italian government.
Khurshid, meanwhile, said the government is studying Italy's decision, its reasons as also implications.
"We will study and take a rightful position... We will take informed position," he told reporters on the issue which has sparked an outrage in Kerala.