Washington urged leaders to "rise above the political differences that divert from the important work of unifying the country", US State Department spokesperson Jen Psaki said in a statement.
Somalia's President Hassan Sheikh Mohamud and his prime minister, Abdiweli Sheikh Ahmed, have been at odds for months, and some lawmakers loyal to the president have pushed a vote of no confidence in Ahmed.
"The United States notes with concern the recent political turmoil in Somalia", Psaki said. "Actions to put forward a parliamentary motion for a vote of no confidence in the prime minister do not serve the interests of the Somali people."
Amid the in-fighting, Washington "does not see the utility" in sending delegates to a summit in Copenhagen on Somalia later this month to bring together foreign donors and the government.
The US warnings follow those by United Nations envoy Nicholas Kay, who said the tension "puts at risk" political goals including a referendum on a new constitution next year, ahead of elections in 2016.
Kay said he was worried about reports that lawmakers were being bribed with cash to vote in a no confidence motion against the prime minster.
The Somali government, which took power in August 2012, was the first to be given global recognition since the collapse of Siad Barre's hardline regime in 1991.
Billions in foreign aid has been poured in, including funding the UN-mandated 22 000-strong African Union force, which has done much of the heavy fighting against Somalia's al-Qaeda affiliated al-Shabaab rebels.
It was hailed as offering the best chance for peace in a generation, replacing a transitional leadership mired in ineffectiveness and rampant corruption.
But political wrangles and reports of corruption have raised concern the government, like the last administration, is blighted by infighting and failing to unite in the face of the threat by the al-Shabaab.
UN chief Ban Ki-moon warned earlier this month on visit to Mogadishu that Somalia risks returning to famine without urgent aid, three years since more than 250 000 people died of hunger with three million people in need of support.