NARATHIWAT, Thailand - Thailand's powerful army chief visited the restive south Tuesday, a day after gunmen killed 11 people at a mosque in one of the worst incidents of a five-year insurgency.

The government ordered General Anupong Paojinda to fly to the troubled Muslim-majority region and bring the culprits to justice, said Suthep Thaugsuban, deputy prime minister in charge of national security.

Gunmen stormed into the mosque in Narathiwat province bordering Malaysia during evening prayers on Monday and sprayed worshippers with bullets, also seriously wounding 12 people, police and the army said.

The attack came amid a sudden flare-up in the insurgency that has left 3,700 people dead since 2004 and just hours after the Thai and Malaysian Prime Ministers agreed to step up cooperation over the region's troubles.

"I have instructed Anupong to go down south to monitor the situation and find the perpetrators. I will not say anything until I have received the official report as it's a very sensitive issue," Suthep said.

He refused to speculate on the reason for the attack or who was behind it, although the government has blamed shadowy Muslim separatist insurgents for most of the violence in the south.

Villagers however blamed security forces for the massacre, saying that the insurgents would not attack a mosque.

In April 2004, 32 people, some suspected rebels, were killed by security forces in a raid on a mosque in the south.

The army confirmed that Anupong would visit Narathiwat province but refused to discuss his schedule or whether he would visit Cho-ai-rong district where the attack took place.

Army spokesman Colonel Parinya Chaidilok said the local hospital was short of blood following a series of attacks in recent days and that military trucks with loudspeakers were urging residents to donate.

"We are calling on all Thais, Buddhist and Muslim alike, to donate your blood for humanitarian reasons because the hospital is now suffering from an acute lack of various groups of blood," the announcements said.

Tensions have simmered in the south since Buddhist-majority Thailand annexed the former ethnic Malay sultanate in 1902.

But the current rebellion began on January 4, 2004 when militants raided an army base, also in Cho-ai-rong district, killing four soldiers and stealing weapons.