"Countries have told us they do not want to pursue Sri Lanka's case. But they want to be seen with the US. Some of them have defence pacts with the US and wider trade links," External affairs minister G L Peiris said.
He said the pro-LTTE diaspora possess large sums of money to run the anti-Sri Lanka campaign in order to win over the Western countries.
"They collected large sums of money during the war. They still own businesses in many countries," Peiris said.
Sri Lanka accused the pro-LTTE diaspora of creating pressure on the UN system to act against it for political reasons.
The US-moved resolution, the third in as many years, is to be put to vote at the UN rights body later this month.
Sri Lanka has condemned the move as a gross interference on its sovereignty.
In the resolution, the US has endorsed recommendations by UN rights chief Navi Pillay for an external probe into charges that Sri Lankan troops killed up to 40,000 civilians during the final months of nearly quarter century civil war against the LTTE that ended in 2009.
The previous two resolutions by the US were adopted with India's support.
Speaking in parliament earlier in the day, Peiris said that Sri Lanka could easily have avoided action at the UN Human Rights Council had it given in to international pressures. "We have a national pride. So we cannot give in," he said.
Meanwhile, the US explained the revised draft text of the resolution to other members and sought their views.