Mrs Gandhi, who was accompanied by party Vice President Rahul Gandhi, told reporters in New Delhi after the meeting with Dr Singh, that they are "shocked, astounded and pained by the attack on our colleagues."
She condemned the Maoist attack on the Congress Parivartan Yatra that led to the death of party leader Mahendra Karma.
The UPA Chairperson said the attack on ordinary party workers is "despicable".
"Naturally we are devastated... It is despicable that ordinary people engaged in political activity were attacked," she said.
The Congress President hoped that the Pradesh Congress Committee Chief Nand Kumar Patel and his son, who are missing since the attack, have not been kidnapped by the Maoists.
Mrs Gandhi also expressed concern over the condition of senior Congress leader V C Shukla, who was injured in the attack.
"Shuklaji has been hit by a bullet in the stomach area," she said.
Sonia Gandhi said the Prime Minister has spoken to Chhattisgarh Chief Minister two hours back who had said he will get back but had still not called.
She said all authorities concerned have been asked to render all support.
Her political secretary Ahmed Patel was also present in the meeting with the Prime Minister.