"The United States strongly condemns the abhorrent attack on a migrant detention facility in Tajoura," State Department spokeswoman Morgan Ortagus said in a statement.

"This tragic and needless loss of life, which impacted one of the most vulnerable populations, underscores the urgent need for all Libyan parties to de-escalate fighting in Tripoli and return to the political process," she said.

She said a political solution was "the only viable path to lasting peace and stability in Libya."

Unlike the United Nations and the European Union, the United States did not immediately urge an investigation into the attack, which tore apart a center for migrants and killed at least 44.

The Tripoli-based Government of National Accord denounced the attack as a "heinous crime" and blamed it on the "war criminal Khalifa Haftar," who launched an offensive in April to seize the capital.

Haftar, who enjoys the support of US allies including Saudi Arabia and the United Arab Emirates, denied responsibility and blamed the government.

President Donald Trump, who is close to Saudi Arabia, raised eyebrows in April when he spoke to Haftar by telephone and praised his role in "fighting terrorism and securing Libya's oil resources."

But the United State still officially backs the internationally recognized government in Libya, which has been torn by conflict since the Western-backed uprising in 2011 toppled dictator Moamer Kadhafi.