(Reuters) - The Kenyan air force has destroyed two al Shabaab camps in Somalia, it said on Monday, in the first major military response since the Islamist group massacred students at a Kenyan university last week.

Al Shabaab denied the camps were hit, saying the air force bombs fell on farmland.

Gunmen from the al Qaeda-aligned group killed 148 people on Thursday when they stormed the Garissa University College campus, some 200 km (120 miles) from the Somali border.

Jets pounded the camps in the Gedo region on the other side of the frontier on Sunday, Kenya Defence Forces spokesman David Obonyo said. The mission was part of efforts to stop fighters from those camps carrying out cross-border raids into Kenya.

Al Shabaab has killed more than 400 people on Kenyan soil in the last two years, including 67 during a siege at Nairobi's Westgate mall in 2013, piling political pressure on President Uhuru Kenyatta that intensified with last week's killings.

Kenya has struggled to stop the flow of militants and weapons across its porous 700-km border with Somalia, and the violence has also damaged the economy by scaring away tourists and investors.

Sheikh Abdiasis Abu Musab, al Shabaab's military operations spokesman, told Reuters that none of its camps were damaged in Sunday's raid, and that the fighter jets had instead struck farmland.