WASHINGTON (AFP) - President Barack Obama on Monday faced escalating criticism of US strikes on Libya from lawmakers worried about an open-ended conflict and possible retaliation modeled on the Lockerbie bombing. But amid broad support for moving against Moamer Gaddafi, it was doubtful that congressional leaders would demand an official debate and vote to authorize military action, as provided for under the US Constitution. On the left flank of Obama's Democratic party, one lawmaker charged that Libya's vast oil reserves, not human rights concerns, had motivated the strikes and sharply criticized the president for skirting formal congressional approval. The move "sends the message to the world that American democracy is deeply dysfunctional," said Democratic Representative Michael Honda, who noted the US Constitution gives only the US Congress the power to declare war. Honda, a senior member of the liberal "Progressive Caucus," charged the Pentagon had acted "based on energy security considerations, which is particularly apparent given Libya's 7th-ranked oil reserves." That "sends the message that America cares little about the human rights and freedoms of people in countries, like the Democratic Republic of Congo, Western Sudan, or Ivory Coast, without critical energy resources," he said. "I demand a serious conversation in Congress before new countries are incautiously invaded and before America's legislative branch is eviscerated further," said Honda. Republican Representative Candice Miller, a senior member of the House of Representatives Homeland Security Committee, said it was "very troubling and unacceptable" that Obama had acted without formal consent from Congress. The president, who left Latin America after discussing the crisis with 18 key lawmakers on Friday, "should immediately return home and call Congress back into session so that this action can be fully debated," she said in a statement. "What other internal conflicts might President Obama decide to engage American armed forces? What standard is he using when making a decision to engage American power? These are vital questions that demand answers before we get further drawn into this and other conflicts that have uncertain outcomes."