Washington (CNN) -- Embattled Libyan strongman Moammar Gadhafi's forces have made significant strides against rebel fighters, as the United Nations is working quickly to pass a resolution authorizing international intervention, a senior State Department official told senators Thursday.
In remarks to the Senate Foreign Relations Committee, William Burns, the undersecretary for political affairs at the State Department, said Gadhafi's forces are only about 160 kilometers (about 100 miles) outside of the rebel stronghold of Benghazi.
"They've made advances taking full advantage of their overwhelming military superiority in military fire power," Burns said.
Burns expressed fear that Gadhafi, now isolated by the world community, could turn to terrorism again.
"I think there is also a very real danger that if Gadhafi is successful on the ground, that you will also face a number of other considerable risks as well -- the danger of him returning to terrorism, and violent extremism himself, the dangers of the turmoil that he could help create at a critical moment elsewhere in the region," Burns told the committee.
Senators, in turn, expressed frustration with the lack of progress by the United States in responding to Gadhafi beyond sanctions and warnings, as the U.S. tries to build international consensus for any military intervention.
"When is that resolution going to happen, after the bloodbath, in the middle of the bloodbath?" asked Florida Republican Sen. Marco Rubio.
The United Nations Security Council is meeting in New York Thursday, debating forceful options that would go beyond a no-fly zone, Burns told the senators. A vote is schedule for Thursday evening.
When Sen. Robert Menendez, D-New Jersey, asked what those options would include, such as targeted air strikes on Gadhafi's weapons, jamming of government radio signals, and using the tens of billions of dollars in Gadhafi's assets that have been frozen, Burns would only say that diplomats are talking about a "whole range of measures," including a number of the steps Menendez mentioned.
"We are pursuing -- along with the Lebanese, the British, French, other partners in the council -- measures that include a no-fly zone, but could go beyond that.," Burns said. "And I can't in this session, since the debate is going on the Security Council right now, go into a lot of detail about that. But there are measures short of boots on the ground that could be taken by the international community, including active air participation."
Burns' remarks echoed White House Press Secretary Jay Carney, who said Thursday that the United States is still "actively considering" the imposition of a no-fly zone over Libya, and that U.S. officials also are examining other options to put pressure on the Gadhafi regime.
With the ground situation evolving in Libya, U.S. Ambassador to the U.N. Susan Rice said previously this week that there are "inherent limitations" regarding a no-fly zone "in terms of protecting civilians."
The U.S. military does not view a no-fly zone as sufficient to stopping Gadhafi. Air Force Chief of Staff Gen. Norton Schwartz told a Senate Armed Services Committee hearing on Thursday that establishing such a zone "would not be sufficient" to stop the gains made by Gadhafi.
Schwartz told the committee that establishing a no-fly zone would take "upwards of a week."
Defense Secretary Robert Gates has cautioned about the use of a no-fly zone in the past weeks, saying it would involve a military attack on Libya to take out air defenses. On Thursday, Pentagon spokesman Col. Dave Lapan said Gates' concern extends to other potential military operations in Libya.
"It would be logical if one of his concerns about a no-fly zone is the element of attacking Libyan air defenses, then an option of air strikes would be pretty similar," Lapan told reporters at the Pentagon.
Burns expects the U.N. Security council to come to an agreement on a resolution Thursday, but wants both operational and financial support from Arab states on the measures decided upon.
"Those are discussions that we've begun including with particular Arab states that have expressed an interest and a willingness to participate in this," Burns said.