Colombo - The US warned Sri Lanka on Tuesday that re-conciliation with ethnic Tamils after the island's separatist war will not be easy, as it praised the new reformist government elected last week.Two senior US diplomats pledged to work with Prime Minister Ranil Wickremesinghe's government during a visit to the island in the wake of the August 17 general election."We recognise that this process is going to take time. Nobody expects miracles," US assistant secretary of state for human rights Tom Malinowski told reporters after talks with Foreign Minister Mangala Samaraweera.But Malinowski said the results of the vote, along with January's presidential poll that swept strongman Mahinda Rajapakse from power, showed Sri Lankans were against "politics of ethnic and religious divisions, against extremism on both sides".Washington had an uneasy relationship with Rajapakse, who defied US pressure to investigate cases of thousands of mainly Tamils who went missing in the final stages of the brutal conflict in 2009.Tremendous progressUS Secretary of State John Kerry visited the island in May to cement stronger ties with President Maithripala Sirisena's administration, which has reached out to the Tamil minority.Assistant secretary of state for South and Central Asian Affairs Nisha Biswal said on Tuesday "tremendous progress" had been made on reconciliation and combating corruption since Sirisena ousted Rajapakse in January. "We have seen not only this enduring commitment to democracy but also a tremendous momentum of progress towards institutions of good governance, towards combating corruption and towards promoting re-conciliation," she said.Sirisena, who appointed Wickremesinghe as prime minister after coming to power, has vowed to introduce democratic reforms and pursue re-conciliation.Rajapakse, who oversaw the crushing of the Tamil rebels in 2009, has come under investigation along with family members for alleged graft during his decade in power. He staged a failed comeback bid at last week's poll in an attempt to become prime minister.The UN Human Rights Council is due to release a report next month on Sri Lanka's alleged war crimes during Rajapakse's time in command. Minister Samaraweera said Colombo was working on an "independent domestic mechanism" to address rights abuses under the former regime, but gave no details.