New Delhi, Apr 15 : Prime Minister Manmohan Singh on Wednesday expressed his concern on the ill-effects of terrorism on the nation and admitted that if the world economy fails to tackle terrorism, it can adversely affect the investment scenario and economic progress of the country.

Meeting with members of the Editor''''s Guild here, Dr. Singh, however, said that the consensus among world leaders is that the global economy will be in a much better position by September.

Dismissing the possibility of holding a composite dialogue with Islamabad, Dr. Singh said there is no hope for discussions until Pakistan dismantles the terror infrastructure within its territory.

"So long as Pakistan chooses to allow its territory to be used against India, no negotiation can take place... We are for engagement with Pakistan but Pakistan must prove its sincerity by bringing the perpetrators of 26/11 attacks to book," he said.

Talking on regionalism in politics, Dr. Singh said that regional parties can act as an obstacle to growth. He said that the country needs a political party with national perspective and a strong and stable government.

He further pointed out that communalism can destroy the country. Singh warned that disaster awaits India if people are divided and even a few adopt the path of terrorism.

Commenting on the ''''personal remarks'''' against him by the Bharatiya Janata Party leader L K Advani, Dr. Singh said his decision to answer back Advani was a conscious choice.

Manmohan Singh, who had repeatedly been called a "weak Prime Minister" by Advani said, "Any serious political observer knows my remarks on Advani are true. I owe it to myself and the people of India to show where the shoe pinches. Enough is enough."

When asked about alliances, Dr. Singh said that the future of Congress and Left parties coming together would depend on circumstances.

Remembering his experiences as a politician, Singh said he has dealt with the Left, RJD''''s Lalu Prasad Yadav, SP''''s Mulayam Singh Yadav, AIADMK supremo Jayalalithaa, the PDP, and had managed them all well. (ANI)