TRIPOLI/WASHINGTON - US President Barack Obama said on Thursday it was inevitable Libyan leader Muammar Gadhafi would have to leave power and only then could a democratic transition in the North African state proceed.

Obama was speaking in a major address about the Middle East where a series of uprisings this year have toppled governments in Tunisia and Egypt and inspired a three-month-old revolt in Libya that aims to overthrow Gadhafi after 41 years in power.

"Time is working against Gadhafi. He does not have control over his country. The opposition has organised a legitimate and credible Interim Council," Obama said in Washington.

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"When Gadhafi inevitably leaves or is forced from power, decades of provocation will come to an end and the transition to a democratic Libya can proceed," he said, defending his decision to take military action against the Libyan leader's government.

His comments echoed those of NATO Secretary-General Anders Fogh Rasmussen who said on Thursday that military and political pressure were weakening Gadhafi and would eventually topple him.

"Obama is still delusional," Libyan government spokesman Mussa Ibrahim told reporters. "He believes the lies that his own government and media spread around the world ... It's not Obama who decides whether Muammar Gadhafi leaves Libya or not. It's the Libyan people."

Libyan state television on Thursday showed footage of the leader.

Acting under a UN mandate, NATO allies including France, Britain and the United States are conducting air strikes that aim to stop Gadhafi using military force against civilians.

In some of the latest strikes, NATO hit Gadhafi's forces around 15 km (9 miles) east of the rebel-held town of Zintan in the Western Mountains region. The town and the port city of Misrata have seen some of the heaviest fighting in recent weeks.

A Reuters reporter in Zintan said NATO strikes on a government weapons depot outside the city sent plumes of smoke into the sky. Government shelling of rebel divisions near the town killed at least one rebel and wounded three, a medical official in the town said.

Rebels control eastern Libya and pockets in the west but the conflict has reached a military stalemate as rebel attempts to advance on Gadhafi's stronghold of Tripoli have stalled.

Western governments, under pressure from sceptical voters, are counting on Gadhafi's administration to collapse.

"We have significantly degraded Gadhafi's war machine. And now we see results, the opposition has gained ground," Rasmussen told a news conference in the Slovak capital, Bratislava.

"I am confident that a combination of strong military pressure and increased political pressure and support for the opposition will eventually lead to the collapse of the regime."