TRIPOLI, Libya – Col. Moammar Gadhafi’s forces intensified attacks in opposition-held cities, creating panic in the town of Misrata, even as U.S. and allied warplanes broadened their airstrikes across Libya, U.S. military officers and eyewitnesses said.

Despite the increasing presence of allied aircraft overhead, Gadhafi has rushed to put down the remaining pockets of the rebellion that has threatened his rule.

In the rebel-held town of Misrata, government forces resumed their assault Wednesday evening despite allied airstrikes for the second day on the outskirts of the city.

Witnesses there said Gadhafi’s tanks closed in on a large medical center used to treat the injured and as a gathering point for the opposition. Rockets fired by Libyan units have landed within 100 yards of the facility.

“The situation is very serious here in Misrata,” said an opposition supporter in the city reached Wednesday evening. “The tanks are coming again to the center of Misrata city and they are bombing the hospital at this time.”

U.S. officers said the U.S.-led campaign is not conducting airstrikes inside urban areas in order to avoid causing civilian casualties. Civilian deaths could undercut political support for the campaign.

“We’re not going into the cities,” a senior U.S. officer said, referring to the airstrikes. “There’s an extra amount of effort placed on preventing civilian casualties by our actions.”

Instead, the allied warplanes are hitting Libyan units outside cities, as well as supply lines and headquarters facilities, in hopes of pressuring them to halt attacks against civilians, the officers said.

But the limitation on the allied strikes also appeared to give Gadhafi’s troops, once they are deployed inside rebel-held cities, freedom to carry out attacks relatively unmolested, at least for the time being.

Rear Adm. Gerard Hueber, a U.S. naval officer involved in directing the air campaign, said U.S. and allied aircraft were extending their operations westward from Benghazi and were now attacking Libyan army targets across the country.

Even so, Hueber conceded that Gadhafi’s forces had intensified their attacks against rebel areas in the last day, despite the stepped-up air campaign.

“In Ajdabiya, regime forces intensified combat in, into and out of the city. In Misrata, regime forces continue to clear opposition, increase combat operations and target civilian populations in the city,” he told reporters at the Pentagon from a ship off Libya’s coast.

The signs that Gadhafi is moving forces and targeting opponents highlights the growing questions about how soon the U.S. will be able to hand off responsibility for the air operation to its allies and whether they will be forced to escalate their confrontation with Gadhafi in order to achieve even the limited goals of deterring his attacks on civilians.

House Speaker John Boehner on Wednesday presented the White House with a series of pointed questions about its U.S. military strategy and goals for the continued campaign.

“I and many other members of the House of Representatives are troubled that U.S. military resources were committed to war without clearly defining for the American people, the Congress, and our troops what the mission in Libya is,” wrote Boehner, R-Ohio.

If Gadhafi’s forces are able to further suppress opposition to his regime without suffering severe losses from the allied airstrikes in coming days, the situation in Libya might turn into a lengthy stalemate, with pockets of opposition in parts of the country but Gadhafi still in power in Tripoli and other areas.

At least four powerful explosions consistent with airstrikes or cruise missile strikes could be heard in central Tripoli on Wednesday at around 11 p.m., apparently from the direction of Gadhafi’s Bab Aziziya residential compound.

The senior U.S. officer offered no timetable for how long the U.S. and its allies were prepared to let the limited airstrikes continue, or how the international effort could be escalated, if Gadhafi defies international calls to withdraw his forces.

Over a 24-hour period beginning at 6 a.m. Tuesday, U.S. warplanes carried out 28 airstrikes, and a small but unknown number were carried out by planes from other countries.

Allied warplanes destroyed two missile sites around Tripoli, the capital, and also hit a government ammunition depot outside the city of Misrata and Libyan Army ground forces around Ajdabiya, the eastern city where large numbers of Libyan troops remain.

A witness in Misrata said the airstrike on the ammunition depot caused an earth-shaking explosion and sent a fireball into the sky early Wednesday morning at around 2. An earlier airstrike targeted the city’s airfield, where troops loyal to Gadhafi had massed.

Ambassadors to NATO met for the third straight day Wednesday to try to work out an agreement on who will assume command of the operation in Libya after the U.S. steps back from the lead. Reports suggested some progress in bridging divisions between alliance members such as Britain and Italy that want NATO to take command, and others, including France and Turkey, that say a NATO command would be politically unwise with regard to public opinion in the Arab and Muslim world.

One compromise envisions the coalition tapping NATO military structures and resources but leaving political command of the mission to another multilateral body.

The cracks in the coalition prompted Germany, which has opposed intervention in Libya, to pull military personnel from NATO aerial reconnaissance teams in the Mediterranean so that they would not be participating in the Libya mission. But Berlin said it would assign 300 more troops to Afghanistan to compensate so that there would be no net effect on NATO personnel.

Despite discord over the no-fly zone, NATO began helping to enforce the arms embargo against Libya. The alliance has sent six warships to waters off the Libyan coast to help “cut off the flow of arms and mercenaries” to the Gadhafi regime, said NATO spokeswoman Oana Lungescu. NATO officials said alliance members have pledged another 16 ships to the effort.