Story highlights A Catholic church and the African Inland Church were attacked, police say

Red Cross and police confirm 40 wounded

Attacks have escalated since Kenyan forces invaded Somalia to battle militants

The grenade attacks have mostly targeted Nairobi, Mombasa and border areas

Explosions targeting two churches in Kenya near the Somali border killed at least 17 people, the Red Cross said, in the latest spate of attacks on the East African nation.

The blasts wounded at least 40 others, the Red Cross said. Regional deputy police chief Philip Ndolo also confirmed the injuries, saying "about a dozen" were critically wounded.

A Catholic church and the African Inland Church were both attacked by people wearing balaclavas and bearing guns and grenades, Ndolo said. The attacks took place about 10 a.m. local time.

No one immediately claimed responsibility for the incidents in the town of Garissa. Most of the dead were from the African Inland Church, Ndolo said, including two police officers who were standing guard.

Sunday's blasts happened at two churches in the Kenyan town of Garissa, close to the border with Somalia.

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The injured were taken to the Garissa Provincial General Hospital, about a kilometer away, he said.

"We condemn these attacks in the strongest possible terms," Ndolo said. "The Kenyan police call for members of the public to come forward with information that will lead to the arrest of the responsible persons."

Additional security forces and police were deployed, and the investigation was under way, he said. "The situation is tense, but under control."

Witnesses have told authorities they saw two attackers at the Catholic church and four at the African Inland Church, he said.

Violence has escalated since Kenyan forces invaded neighboring Somalia last year to battle Islamist militant group al-Shabaab, which it blamed for kidnappings of foreigners in the nation.

When Kenya pursued the militants, the terror group threatened retaliatory attacks, saying it considers the incursion an affront to Somalia's sovereignty.

Since the invasion in October, Kenya has been hit by a series of grenade attacks blamed on al-Shabaab or its supporters.

The grenade attacks have mostly targeted the capital of Nairobi, the port city of Mombasa and northeastern towns and refugee camps near the border with Somalia.

Garissa is close to the Somali border and the Dadaab refugee camp, where gunmen kidnapped four aid workers and killed a driver last week.

Al-Shabaab is linked to al Qaeda and has been designated a terrorist organization by the United States.

U.S. officials have issued warnings of potential attacks in the country since the incursion.