Embattled Libyan leader Moammar Gadhafi reached out to the U.S. on Wednesday, sending a letter to President Barack Obama asking him to halt the NATO military campaign in his country.

NATO has been on a mission to enforce a no-fly zone and protect civilians from attack by pro-Gadhafi forces. NATO jets have destroyed much of the Libyan air force's firepower.

In Gadhafi's three-page letter, he calls the U.S. president "our son" and describes the mission as an "unjust war against a small people of a developing country."

The rambling communique, which was sent to the State Department and forwarded to the White House, also wishes Obama good luck in next year's presidential election and strikes a conciliatory tone.

"To serving world peace ... Friendship between our peoples ... and for the sake of economic, and security co-operation against terror, you are in a position to keep NATO off the Libyan affair for good," Gadhafi writes in the letter, obtained by The Associated Press.

While the White House confirmed that the letter had been received, an official said the ceasefire request could not be met at this time.

"The conditions the president laid out are clear," White House press secretary Jay Carney told reporters.

The news Wednesday came on the same day a former U.S. congressman arrived in Libya for talks with Gadhafi. Curt Weldon, who was personally invited by Gadhafi, described the trip as a private mission to urge the longtime leader to step down.

He said he had informed the White House about the trip as well as some members of Congress. It wasn't clear whether Gadhafi's letter to Obama was linked to Weldon's visit.

Weldon has been to Libya on two previous occasions.

Shifting ground war strategies

Earlier Wednesday, stung by more than two weeks of aerial bombardments, forces loyal to Gadhafi began adjusting their tactics and frustrating rebel attempts to retake a key oil port in the process.

Rebel forces are trying to fight their way back into the eastern oil port of Brega. They had taken control of the town with the support of an aerial bombardment on Monday, but a barrage of rocket and artillery fire from pro-Gadhafi forces turned them on their heels Tuesday.

As the rebels fled as far as Ajdabiya, several dozen kilometres away, there did not appear to be any immediate response from international aircraft patrolling the skies.

"When you see this, the situation is very bad. We cannot match their weapons," 64-year-old retired soldier-turned-rebel militia Kamal Mughrabi told The Associated Press. "If the planes don't come back and hit them, we'll have to keep pulling back."

But French Foreign Minister Alain Juppe said Wednesday that air strikes are more difficult now that a large portion of Gadhafi's aircraft and armoured vehicles have been destroyed.

As a result, pro-Gadhafi forces left on the ground are harder to distinguish from the deserters who have joined the rebel militia. Gadhafi's forces are also said to be entrenched in residential areas of the besieged western city of Misrata, effectively taking cover among the civilian population.

"They snuck their anti-aircraft weapons and tanks into the city. They are between the apartment buildings and the trees," a doctor speaking on condition of anonymity told the AP. "They disguise their equipment on the big agricultural trucks that the farmers use outside of town. They bring in mortars with civilian cars."

Reporting from Benghazi, CTV's Janis Mackey Frayer says the situation underscores the current, challenging phase of the international military mission that began on March 19.

"There are only so many targets that would fall within the mandate of the NATO air campaign," she said, explaining that the mission is primarily aimed at protecting Libya's civilian population.

"Gadhafi forces are said to be sticking close to civilian centres," she added. "So the more integration, the tougher it is for these air strikes to realize their goals and not have collateral damage."

On Tuesday, Brig. Gen. Mark Van Uhm of NATO said UN-sanctioned air strikes had destroyed as much as one-third of Gadhafi's weapons, as he promised the aerial missions would continue.

Whether the planes can actually attack their targets is another question, however, as he noted three-quarters of the scheduled missions ended without dropping any bombs or missiles as the pilots were unable to distinguish between fighters and civilians.

Whatever the reason, Mackey Frayer said the change from the frequent bombardments in the early days of the international campaign is frustrating some.

The rebels fighting to oust Gadhafi have nevertheless marked a number of significant advances, including official recognition of their transitional council by the governments of France, Italy and Qatar.

The rebels are also trying to ship their first tanker load of oil from the eastern city of Tobruk.