Indian Prime Minister Narendra Modi's ruling party won power in remote northeast Assam and made gains in other states on Thursday, expanding its political influence beyond its traditional heartland two years after a landslide national election victory. The Hindu nationalist Bharatiya Janata Party seized control of restive Assam from the centre-left Congress party, which promised to "work harder" to win people's confidence after losing ground in several states. "These results show that the people are accepting, appreciating and supporting our pro-development ideology," Modi told supporters at his party's headquarters in New Delhi. Assam is the first northeastern state to be controlled by the BJP, whose traditional power base is in Hindi-speaking north, central and west India. Political analyst Ashok Malik said that Thursday's results showed the BJP was now India's only truly national party. "This expansion for the BJP comes at a time when the Congress is shrinking, even though they have different social constituencies," said Malik, a fellow with New Delhi-based Observer Research Foundation think-tank. "And now, the BJP is the only pan-India national party, which the Congress once used to be." The BJP needs to win state elections to gain more seats in the nation's upper house of parliament, which has been blocking reforms seen as crucial to fueling the economic growth it has promised voters. Most members of the upper house, which has obstructed measures such as a planned standardised goods and services tax, are indirectly elected by state legislatures. The BJP mounted a fierce campaign in tea-growing Assam, promising to support indigenous rights and crack down on illegal immigration from neighboring Bangladesh. Migrants have long been accused of illegally entering the state from Bangladesh and grabbing land, causing tensions with local people and sporadic outbreaks of communal violence. India's seven northeastern states, joined to the rest of the country by a narrow sliver of land, are culturally distinct from the rest of the country and have a long history of separatist insurgencies. "People were fed up and they wanted a change... that's why this time they've voted for BJP and its alliance partners," said Sarbananda Sonowal, BJP's Assam chief ministerial candidate. Partial results showed Congress had just 26 of the total 126 seats in Assam and the BJP-led alliance had 86. The party also made gains in Kerala in the south and in eastern West Bengal state, whose feisty chief minister Mamata Banerjee's Trinamool party had won a clear majority even before all the votes were counted, despite corruption allegations. Modi's party swept to power in a general election two years ago promising business-friendly reforms to overhaul the economy, but lost out in two critical state polls in 2015. With final results from the five states still to come in, regional parties looked set to win in Kerala and Tamil Nadu in the south. Jubilant supporters of Tamil Nadu's popular Chief Minister Jayalalithaa Jayaram gathered outside her house to celebrate, many of them painted in the colours of the state flag. The former movie star known as "Amma" (Mother) has long enjoyed a huge following in prosperous Tamil Nadu where she has won three terms as chief minister since 1991. The 68-year-old has earned loyalty with a series of populist schemes including giving away gold, goats and kitchen appliances at election time, but has also drawn accusations of corruption and an autocratic governing style. This year, her AIADMK (All India Anna Dravida Munnetra Kazhagam) party's election manifesto promises included free wi-fi at public places, laptops for students, free cell phones and minimum units of free electricity every month. Congress vice president Rahul Gandhi, who fronted the campaigning in several states, tweeted that his party would "work harder till we win the confidence & trust of people." Rahul's mother Sonia, who is the Congress president, said in a statement: "We will introspect into the reasons for our loss and rededicate ourselves to the service of the people with greater vigor." The party, in power nationally until 2014, was leading in only one state — the southern Indian seaside town of Puducherry, a former French colony with less than a million eligible voters.