Releasing the Congress manifesto for 2009 Lok Sabha polls along with party President Sonia Gandhi [ Images ], he termed BJP's defence of Varun Gandhi's [ Images ] comments with communal overtone as shameful.
He said Left parties and BJP have a 'negative mindset', which cannot take the nation forward.
NDA and Third Front do not have the capacity to meet the challenges facing the nation, Dr Singh said.
He reminded people of the "historic opportunity" to decide the path they would like to follow in the next five years.
The prime minister said if the country had a strong and purposeful government, 'India can be a source of inspiration to rebuild more prosperous and more equitable South Asia'.
The prime minister expressed anguish over the instability in neighbouring countries. "If I look at the challenges around India [ Images ], I see instability," he said.
He said Pakistan was facing terrorism and pointed out at events in neighbouring Nepal, Bangladesh and Sri Lanka [ Images ].
"These are all events which cause worry about future of South Asia," he said.
The prime minister said the Congress President has explained why it was necessary for the party to come back to to power to meet the enormous challenges the country faced.
"When I look at the opportunities, I am convinced that this country can move forward on road to faster growth", he said, adding the benefits of developments can be passed on to each section of society, particularly Scheduled Castes, Scheduled Tribes and minorities.
He said under Gandhi's leadership, the UPA has worked tirelessly to fulfil the promises made in the Common Minimum Programme and the Congress manifesto.
"We still believe that diplomacy should be given a chance," he said adding that no purpose would be served by creating a war hysteria.
The prime minister said diplomatic efforts have succeeded and for the first time Pakistan has admitted that its citizen was involved in the horrible act.
"I can't say we are fully satisfied with actions taken by Pakistan in connection with Mumbai attacks," he said, adding that Pakistan must take next consequential steps to ensure perpetrators of Mumbai attacks are brought to justice.
To a question as to who was the main adversary of the Congress in the ensuing polls -- BJP or the Third Front -- he said in politics, all adversaries should be taken seriously.
"But we are prepared to meet the challenges both Right as well as the Left," he said, adding that communalism was the greatest challenge.
"If we do not roll back communal forces, India's unity, integrity and prosperity will be in danger," he said.
To a question on the Sachar committee recommendations on the welfare of Muslims, the prime minister said many of the suggestions have been accepted particularly on education of children, especially girls.
Observing that much needed to be done, he said though the quota of minorities in government jobs has been increased, efforts should be made to increase it further.
Asked how he felt on being projected as the prime ministerial candidate outside the Nehru-Gandhi family, Dr Singh said it was a great honour and great privilege for him.
He expressed confidence that the government would do better in the future under the leadership of Gandhi.
Turning to economy, the prime minister said economic activities would be revived in a big way in the next six to seven months due to the stimulus package announced by the government.