TRIPOLI, Libya — Moammar Gadhafi’s forces battled poorly armed rebels Tuesday for control of towns near the capital trying to create a buffer zone around his seat of power. The increasingly violent clashes threatened to transform the 15-day popular rebellion in Libya into a drawn-out civil war.

Amid the intensified fighting, the international community stepped up moves to isolate the longtime Libyan leader.

U.S. Defense Secretary Robert Gates said he ordered two ships into the Mediterranean, including the amphibious assault ship USS Kearsarge, and he is sending 400 Marines to the vessel to replace some troops who left recently for Afghanistan.

Military leaders weighing a no-fly zone over Libya said it would be a complex task that would require taking out Gadhafi’s air defenses. Russia’s top diplomat dismissed the idea as “superfluous” and said world powers should focus on sanctions.

Gadhafi’s son, Seif al-Islam, warned Western forces not to take military action against Libya and said the country is prepared to defend itself against foreign intervention.

“If they attack us, we are ready,” he told Sky News, adding that the Gadhafis are ready to implement reforms.

Facing an unprecedented challenge to his 41-year rule, Gadhafi’s regime has launched the bloodiest crackdown in a wave of uprisings against authoritarian rulers in the Middle East. Gadhafi has already lost control of the eastern half of the country but still holds Tripoli and other nearby cities.

An exact death toll has been difficult to obtain in the chaos, but a medical panel in the eastern city of Benghazi, where the uprising began Feb. 15, said at least 228 people had been killed, including 30 unidentified bodies.

U.N. Secretary General Ban Ki-moon has cited reports that perhaps 1,000 have died in Libya.

Secretary of State Hillary Rodham Clinton told Congress that the U.S. must lead an international response to the crisis, including expanding already tough financial and travel sanctions against Gadhafi, his family and confidants and possibly imposing a no-fly zone over Libya.

“Libya could become a peaceful democracy, or it could face protracted civil war. The stakes are high,” she said.

Gadhafi’s regime has retaken at least two towns and threatened a third, while rebels repulsed attacks on three other key areas – Misrata to the east, Zawiya to the west, and the mountain town of Zintan to the south of the capital.

One of those retaken was the strategic town of Gharyan, the largest in the Nafusa Mountains, overlooking Tripoli, a resident said, asking to be anonymous for fear of government retaliation.