Sri Lanka's separatist rebels used light aircraft to bomb an army defense line in the island's war-torn north early Sunday but didn't cause any casualties, the military said.

Military spokesman Brig. Udaya Nanayakkara said the Tamil Tiger rebel plane dropped three bombs near Sri Lankan forces in the Welioya region but no soldiers were hurt.

It was the first attack by the rebels' air wing — made up of a few self-assembled light aircraft — since it helped insurgents on the ground attack a government air force base last October. The government lost eight planes in that assault.

On Saturday, Sri Lankan fighter jets pounded a rebel artillery position in Welioya, the military said in a statement.

Rebel spokesman Rasiah Ilanthirayan was not immediately available for comment Sunday.

Meanwhile, police said they arrested nine suspects in connection with a bus bombing that killed 26 passengers outside Sri Lanka's capital on Friday.

President Mahinda Rajapaksa said Saturday the blast proved the Tamil Tiger separatists were facing growing pressure on the battlefield in the north.

"The terrorists had once again resorted to killing innocent civilians in the face of heavy setbacks on the battlefield," Rajapaksa said in a statement.

Friday's bomb tore through a bus filled with rush-hour passengers in Piliyandala, a suburb of the capital, Colombo. Among those killed were a Buddhist monk and a 10-year-old child, the government said. Another 64 people were wounded.

Police spokesman N.K. Ilangakoon said the nine suspects were being questioned. He did not give more details.

The military said it fears more rebel attacks against civilians as the northern war front heats up.

The government has stepped up attacks on the Tamil Tigers' de facto state in the north since pulling out of a long-ignored cease-fire in January. It claims to have killed thousands of guerrilla fighters since then. The rebels deny those casualty figures and have managed to fend off numerous offensives.

The rebels have fought since 1983 to create an independent homeland for minority ethnic Tamils, who have been marginalized by successive governments controlled by Sri Lanka's Sinhalese majority. More than 70,000 people have been killed in the violence.