The leaders of Afghanistan and India have signed a strategic partnership agreement during a visit by President Hamid Karzai to Delhi.Mr Karzai met Indian PM Manmohan Singh, who said violence in Afghanistan was undermining security in South Asia. He also said that India would "stand by Afghanistan" when foreign troops withdraw from the country in 2014. Mr Karzai's visit follows a series of attacks which have damaged ties between Kabul and India's rival, Pakistan. Correspondents say the increasingly close relationship between Kabul and Delhi will be viewed with some suspicion by Pakistan, which sees Afghanistan as its backyard.