Two weeks after a barrage of mostly U.S. missiles and bombs opened the international air assault on Libya's Moammar Gadhafi, the American combat role is ending, the rebels are reeling, and the Pentagon is betting European allies can finish the job.

Gadhafi is standing, with a few uncertain signs that his inner circle could crack.

The Obama Administration is hoping that if Gadhafi's government doesn't implode soon, a relentless campaign of airstrikes on his tanks, air defenses, and his most trusted army units at least will weaken his ability to survive a renewed uprising by a disjointed opposition.

The rebels initially rattled Gadhafi but in recent days have given up most of their gains.

The bottom line, according to Adm. Mike Mullen, chairman of the Joint Chiefs of Staff: "He's still killing his people."

So the mission remains incomplete, but the United States is following through on a pledge to shift the main combat burden to Britain, France, and other NATO allies.

Starting today, no U.S. combat aircraft are to fly strike missions in Libya. NATO's on-scene commander can request U.S. strikes, in which case they may have to be approved in Washington.

U.S. combat aircraft flew 24 strike missions Saturday in Libya, the Pentagon said.

Also withdrawing from the combat mission today will be the initial workhorses of the military campaign: U.S. Navy destroyers and submarines that launched Tomahawk cruise missiles from positions in the Mediterranean Sea.

No Tomahawks were fired Saturday, the Pentagon said.

With the shift of the U.S. military's role, U.S. planes and naval vessels will be on standby in case NATO commanders decide their forces cannot handle the mission alone.

Combat air missions will continue to be flown by Britain, France, and other NATO member countries.

A larger group of participating air forces will patrol over Libya to ensure Gadhafi's air force stays grounded. U.S. planes will support them with refueling aircraft and electronic jammers.

The Navy began the operation March 19 with 11 ships in the Mediterranean. As of Friday, nine remained.

The international military mission has been limited from the start, with the stated objective of protecting Libyan civilians from attack.

But until this weekend's U.S. stand-down, Air Force and Marine attack planes have chased down Libyan tanks and other targets daily.

Meanwhile, deadly battles in Libya forged ahead Sunday as pro-government forces shelled a medical clinic in the city of Misrata, killing one person and wounding 15 others, a hospital source said.

The source, a doctor who was not identified for security reasons, told CNN two people were injured by an initial mortar blast. The rest were wounded by a second mortar blast when they went to the scene of the first attack to help victims.

One of the injured is a 14-year-old child who suffered a fractured skull and is in a coma, the doctor said Sunday.

The clinic that was attacked had evacuated patients because of recent attacks, said another doctor at a Misrata hospital that received the patients. But it was being guarded by opposition "fighters and young people" who were injured.

The blasts were among the latest attacks in Libya, where the power struggle rages on between forces loyal to leader Moammar Gadhafi and opposition members seeking an end to his four-decade rule.

NATO airstrikes hit several rebel vehicles and killed at least 13 rebel fighters, spokesmen for the Libyan opposition said Saturday. Seven others were wounded.

"Based on the information we have, they (the opposition forces who were hit) heard the airstrikes and went ahead to see what the damage was, and that's when they got hit," rebel spokesman Shamsiddin Abdulmolah said. "They were told to stay back, but they jumped the gun."

NATO was investigating the incident, a spokeswoman said Saturday.

"NATO takes any reports of civilian casualties very seriously, but exact details are hard to verify as we have no reliable sources on the ground," NATO's Oana Lungescu said.

Notions of a cease-fire in Libya quickly faded as a battle for control continued Saturday in the oil town of al-Brega. It was not immediately clear who commanded control Saturday of the coastal city that has changed hands six times in as many weeks under the dramatically shifting circumstances of the Libyan war.

Forces loyal to Gadhafi showed no signs of backing down after officials spurned an opposition cease-fire proposal.

U.S. officials claim Gadhafi's military capabilities have been steadily eroded since the onset of U.N.-sanctioned airstrikes.

The dictator's forces, however, still outnumber rebels by about 10 to 1 in terms of armor and other ground forces, according to Navy Adm. Mike Mullen, the Joint Chiefs of Staff chairman.