Tripoli, Libya (CNN) -- Tanks from both pro-government and opposition sides headed toward each other Saturday in the Libyan city of Benghazi as families -- fearing a massacre by the government -- fled the rebel stronghold.
Meanwhile, longtime Libyan ruler Moammar Gadhafi sent firm messages to world leaders after the U.N. Security Council voted to allow the use of force to protect civilians as the Libya's civil war rages on.
"I have all the Libyan people with me ... and they are prepared to die for me -- men, women and even children," Gadhafi said in a letter addressed to U.S. President Barack Obama and other world leaders. The letter was read publicly Saturday by government spokesman Musa Ibrahim.
Early Saturday, a fighter jet plummeted from the sky and burst into flames and artillery fire fell in Benghazi.
Footage showed the plane engulfed in fire as it nose-dived to the ground. An opposition fighter said the plane belonged to the rebels and was dispatched to try to stop forces supporting Gadhafi from entering Benghazi.
CNN could not independently confirm who the plane belonged to.
A day earlier, the government said it was abiding by a cease-fire ordered by the United Nations, but witnesses have said violence from pro-Gadhafi forces has continued.
Benghazi is particularly important to the opposition because rebels have been been pushed back from other cities. They have vowed to defend Benghazi at all cost.
Violence has raged in Libya following protests calling for democracy and freedom and demanding an end to Gadhafi's almost 42-year-long rule. Protests have been met by widespread reports of violence by Gadhafi forces.
Rebel fighters -- which include members of the military who defected -- have said they had to take up arms and fight back or face being killed.
But Gadhafi has repeatedly said the country is actually fighting al-Qaeda.
"We could never -- and we would never -- fire one bullet against our people," Gadhafi said in a letter directed to Obama, U.N. Secretary-General Ban-Ki-moon, French President Nicholas Sarkozy and British Prime Minister David Cameron.
"You have no right -- ever -- to intervene in internal affairs," the letter also said. "You will regret it if you take a step towards intervening in our internal affairs."
The U.N. Security Council voted Thursday to authorize "states to take all necessary measures to protect civilians." It also imposed a no-fly zone, banning all flights in Libyan airspace -- except those that involve humanitarian aid and the evacuation of foreign nationals.
In televised remarks Friday, Libyan Foreign Minister Moussa Koussa said the country decided on "an immediate cease-fire and the stoppage of all military operations."
He urged observers from China, Malta, Turkey and Germany to come "as soon as possible ... to make sure that there is a real cease-fire on the ground."
Deputy Foreign Minister Khaled Kaim said government forces were attacking "armed rebel militias," not civilians.
Kaim also said Gadhafi forces are not fighting a militia group that is making advances in the eastern town of al-Migrun and said the media are distorting Libyan military actions.
He said the country has evidence of "crimes against humanity conducted by the rebels."
But witnesses in the western city of Misrata said earlier Friday that a pro-government assault persisted, and casualties were mounting.
At least 28 people died and hundreds were wounded in fighting in the cities of Misrata, Ajdabiya and Zintan on Friday, according to Khaled el-Sayeh, a military spokesman for the opposition.
"What cease-fire?" asked a doctor in Misrata, who described hours of military poundings, casualties and dwindling resources to treat the wounded. "We're under the bombs."
An opposition member said Friday that "Misrata is on fire," adding that Gadhafi's regime announced a cease-fire to buy itself more time.
"Please help us," he pleaded.
Outside Ajdabiya in eastern Libya, fighters who said they didn't trust Gadhafi said they believe that the declaration was a sham as sounds of explosions pierced through the air.
On Friday, Obama warned Gadhafi to pull back from several besieged cities or face military consequences. But he insisted American troops will not be deployed in Libya.
Obama also said power and water must be restored to several cities.
"These terms are not negotiable," Obama said.
If Gadhafi doesn't comply, the U.N. resolution will be imposed through military action, the president said.
The U.N. resolution, while not authorizing such a move, does not preclude the United States from arming rebels, said Susan Rice, U.S. ambassador to the United Nations.
When asked whether the United States was planning to provide weapons to the opposition, Rice said, "We are focused immediately on protection of civilians, on ensuring that the march to Benghazi does not continue and that those who are most vulnerable have the rights and protections that they deserve."
Discussion about speedy military action against Gadhafi's regime surfaced Friday in Europe and North America.
Countries such as Britain, Spain and Canada have started mobilizing military equipment and personnel in preparation to intervene.
British Prime Minister David Cameron said the United Kingdom has started preparations to deploy aircraft, and "in the coming hours," they will move to air bases where they will be positioned for any "necessary action."
Other nations, including Spain and Canada, said they will provide forces and fighter jets, respectively.
CNN's Arwa Damon, Nic Robertson, Richard Roth, Tommy Evans, Elise Labott, Al Goodman, John King, Alan Silverleib, Raja Razek, Jennifer Rizzo, Joe Vaccarello, Yousuf Basil and Reza Sayah and journalist Mohamed Fadel Fahmy contributed to this report.