TOBRUK, Libya — Moammar Gadhafi’s forces captured the last rebel-held town west of Tripoli after a heavy barrage of tank and artillery fire today as regime forces pressed forward in the east.

The victory in Zwara, about 30 miles from the Tunisian border, solidifies Gadhafi’s hold in his western stronghold, reversing gains made by rebels in several cities early in the uprising against his rule that began on Feb. 15.

Gadhafi’s gains in recent days have increased pressure on the U.S. and other Western powers to intervene to stop the bloodshed.

The Obama administration on Monday held its first high-level talks with the Libyan opposition and introduced a liaison to deal full time with their ranks. But it remained undecided about exactly how much support to lend a group it still knows little about while turmoil and uncertainty increase across the Arab world.

Government troops surrounded the town of 45,000 on Monday and bombarded it with tanks and artillery for hours starting in the morning, killing at least four rebel fighters, several residents said.

Rebels conceded that Zwara had been taken by government forces on today, although sporadic street battles were ongoing.

Most of the fighting was concentrated in the seaside suburbs of the town, leaving residential buildings pockmarked from shrapnel, one rebel said. Most civilians had fled.

The fighter, who spoke on condition of anonymity for fear of reprisals, said rebels were tossing dynamite and shooting at army troops patrolling the town in cars packed with seven to 10 soldiers, many sitting in the open trunks of the vehicles. But he said the attacks were designed to wear down Gadhafi’s better-equipped forces, not to defeat them.

“You can’t fight an organized army that has tactics and military preparation. But we have people ready to die — our will is greater — and in the end, every oppressor has an end,” he said in a telephone interview, as celebratory gunfire from Gadhafi’s forces rang out in the background.

Another fighter in Zwara said the rebels were still in “shock” and were quietly walking about town in civilian clothing, trying to assess the situation.