WASHINGTON- US senators said Wednesday they planned to move quickly to confirm the first US ambassador to Myanmar in two decades, as they pushed to allow investment in the country's oil and gas sector.

President Barack Obama on May 17 nominated Derek Mitchell, a veteran US policymaker on Asia, as ambassador to the country after dramatic reforms including the election of opposition leader Aung San Suu Kyi to parliament.

At a hearing on the nomination, senators across party lines voiced support for Mitchell. Senator Jim Webb, who heads a subcommittee on East Asia, said he hoped to complete Mitchell's confirmation by the end of the week.

But senators pressed the Obama administration to allow investment by US energy companies as part of its loosening of sanctions on Myanmar, voicing fear that US companies would lose out to foreign competitors.

Senator James Inhofe, a Republican from Oklahoma and champion of the fossil fuel industry, said he heard rumors that the administration will exclude oil firms from new rules allowing US investment in the country formerly known as Burma.

"This or any other 'carve-out strategy' would be a strategic mistake," Inhofe told the hearing of the Senate Foreign Relations Committee.

"I believe that US companies including the oil and gas companies can play a positive role in the effort by demonstrating high standards of responsibility, responsible business conduct and transparency -- including respect for human rights in Burma," Inhofe said.

Human rights groups have long charged that the oil and gas industry fuels abuses inside Myanmar, with villagers allegedly forced into labor and the powerful military seizing the revenue to support its operations. Suu Kyi, paying a historic tour of Europe, said in Geneva on June 14 that foreign firms should not partner with the state-owned Myanmar Oil and Gas Enterprise until her country signs up to international standards such as the IMF code on transparency.

In a rare note of discord with Suu Kyi, a Nobel peace laureate who is widely respected in Washington, Webb said that the United States "does not require countries to endorse this code or other standards as a prerequisite for US investment."

Webb, a longtime advocate of engagement with Myanmar, said that other countries as diverse as China and New Zealand have also not signed the code.

Mitchell said that the administration had not made a decision on oil and

gas investment in Myanmar but reiterated concerns about the state-owned company.

US engagement with Myanmar must benefit reform and ensure "that we are contributing to the highest values and that we model the type of behavior that we like to see," Mitchell said.

Not all US lawmakers are enthusiastic about oil and gas investment, with some members of the House of Representatives saying that Myanmar's reforms are overblown.

Senator John Kerry, the chairman of the Senate Foreign Relations Committee, said that any further removal of sanctions needed to be "handled in a thoughtful, step-by-step process that is contingent upon continued progress."

Mitchell, testifying before the committee, warned that reform in Myanmar "is not irreversible" and raised concerns that "hundreds of political prisoners" remained locked up.

He also expressed worries about human rights in ethnic minority areas, pointing to recent violence between Buddhists and Muslims in western Rakhine state that has left more than 80 people dead.

"Recent sectarian violence in Rakhine State demonstrates the divisiveness in Burma cultivated over many decades, if not centuries, that will need to be overcome to realize lasting peace and national reconciliation in the country," Mitchell said.

But he praised President Thein Sein, a general turned civilian who took office last year, as a "remarkable figure."

"We should never forget to recognize his extraordinary vision and leadership and the many reformist steps he and his partners in government have taken over the past year," Mitchell said.