WASHINGTON — Fighters for the Islamic State militant group have been training in remote areas of Libya, heightening the Obama administration’s concern about a country that U.S. officials have largely ignored since its 2011 revolution.

Training camps with several hundred Islamic State fighters have been spotted in parts of eastern Libya, and some U.S. intelligence reports suggest a new presence for the militant group near Tripoli, in the country’s west, U.S. officials disclosed in recent days.

Although the officials say no immediate military response is planned, the appearance of the camps is giving new impetus to a debate about whether the United States eventually will need to expand its campaign against the militants beyond Iraq and Syria.

Islamic State “is exploiting vast, ungoverned spaces in Libya,” Sen. Marco Rubio, R-Fla., said this week during a Senate hearing aimed at coming up with a new legal authorization for U.S. military involvement in the Middle East.

In 2011, the Obama administration organized the NATO air campaign that led to the downfall of former Libyan leader Moammar Gadhafi and the country’s dissolution into a many-sided civil war. President Barack Obama, in an interview in August, said the failure of the U.S. and its allies to do more for Libya after Gadhafi’s fall was his biggest foreign policy regret. Even so, U.S. officials have largely left efforts to broker peace in the country to European officials and have been deeply resistant to the idea of a renewed U.S. military role.

But the growth of a terrorist threat in a chaotic country about the size of Texas stirs alarm in Washington. Such a threat was a chief danger cited by critics of the 2011 intervention, including former Defense Secretary Robert M. Gates.