Grenade attacks on Kenyan churches leave 16 dead

• NEW: Garissa is near the Somali border
• The number of injuries in the explosions at Garissa town is unclear
• Attacks have escalated since Kenyan forces invaded Somalia to battle militants
• The grenade attacks have mostly targeted Nairobi, Mombasa and border areas

(CNN) -- Blasts hit two churches in northeastern Kenya on Sunday, leaving scores injured in the latest attack in the East African nation, the Red Cross said.

The exact number of injuries in the explosions at Garissa town was unclear, the Red Cross said.

CNN affiliate NTV said the blasts killed at least nine people, but CNN was not able to independently confirm the report.

No one immediately claimed responsibility for the incidents.

Attacks have 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 with retaliatory attacks, saying it considers the incursion an affront to Somalia's sovereignty.

Since the invasion in October, Kenya has been targeted 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.

CNN's Faith Karimi and Elizabeth Joseph contributed to this report