US Secretary of State Hillary Clinton headed Wednesday to the southern Indian port of Chennai, a focus of US trade and investment, on the second leg of her trip to the emerging Asian giant. Clinton is expected to deliver a policy speech and meet the chief minister of Tamil Nadu state, which is home to a flourishing Ford factory producing small cars for the booming domestic market. On Tuesday, the top US diplomat met Indian leaders including Prime Minister Manmohan Singh and Foreign Minister S.M. Krishna to push for easier access to the country\'s nuclear market and closer security cooperation. She stressed that the US-India relationship, which President Barack Obama described as the \"defining partnership of the 21st century\", had made great progress in recent years, but was yet to fulfil its potential. Clinton singled out civil nuclear energy as an area where the countries \"can and must do more\" amid frustrations that private US nuclear energy firms are losing out in India to their state-owned French and Russian competitors. As well as lobbying for US commercial interests, the trip to India is also about balancing the delicate relationships Washington maintains with violence-wracked South Asian countries. Clinton said she was \"encouraged\" by India and Pakistan\'s decision to restart their stop-start peace process, but she also heard Indian worries that a planned US troop drawdown in Afghanistan could lead to instability. After triple blasts in Mumbai last week that left 19 people dead, security was foremost among the subjects discussed in New Delhi. India and the US have repeatedly called on Pakistan to crack down on militant groups which are thought to use \"safe havens\" to plan and execute attacks on Indian soil and in Afghanistan. Washington\'s relations with Pakistan -- a crucial counter-terrorism ally -- have deteriorated since US commandos shot and killed Al-Qaeda leader Osama bin Laden on May 2 in a Pakistani garrison town, sowing distrust on both sides. Krishna reminded Clinton that India, which has spent billions of dollars on aid to Afghanistan, had much to lose by instability in the country as a result of the planned US troop withdrawal. The United States has announced plans to withdraw 33,000 surge troops by the end of September 2012, with the first 10,000 due to depart this year. \"It is necessary for the United States to factor in Afghanistan\'s ground realities so that... Afghanistan will be in a position to defend itself against terrorism sponsored by the Taliban,\" Krishna said. Clinton\'s two-day trip follows Obama\'s visit in November -- a courtship of India that reflects the rapid growth in the country\'s economy and a shift in power to emerging nations as a result of the global financial crisis. Commerce has been booming, with bilateral trade up by 30 percent to nearly $50 billion in 2010.