Taliban militants attacked a police checkpoint in southern Afghanistan and killed 16 officers, the Interior Ministry said Monday. Seven Afghan police and soldiers were killed in attacks elsewhere.

Spain's King Juan Carlos, meanwhile, made an unannounced visit Monday to Spanish troops based in western Afghanistan, the royal palace said.

The policemen were manning a checkpoint in the Maywand district of Kandahar province on Saturday when a large group of militants attacked them, said Zemerai Bashary, the Interior Ministry spokesman.

"We still have not found the bodies, but police in Kandahar have launched a search operation," Bashary said.

A Taliban spokesman, Zabiullah Mujahid, said the militant group was responsible for the killings.

The militants have repeatedly attacked the checkpoint — situated near Highway 1, Afghanistan's main thoroughfare — over the last year, part of the reason so many police were stationed there.

The acting police chief of Kandahar province, Omar Khan, said police were investigating and he couldn't give any details about the attack.

Violence in Afghanistan this year reached the highest level since the ouster of the Taliban in 2001. More than 6,300 people died in the insurgency, according to an Associated Press count based on figures from Afghan and Western officials.

Taliban fighters have shied away from attacking international military forces and even the Afghan army, which is better trained and better equipped than Afghan police.

The police, though, have borne the brunt of Taliban attacks.

More than 850 police officers have been killed in attacks since March — the beginning of the Islamic calendar — said Bashary. That represents more than 1 percent of the countrywide police force of some 73,000 officers.

Elsewhere, four Afghan soldiers were killed in a mine explosion Sunday in Uruzgan province, while one soldier was killed in Paktia province in another blast, the Ministry of Defense said in a press release.

In Helmand province, a roadside bomb exploded Monday against a police vehicle driving through Musa Qala, killing two officers, said Musa Qala district chief Haji Bir Mohammad.

In the country's west, Carlos traveled with the defense minister and head of the joint chiefs of staff to the Spanish base in the city of Herat.

Spain has some 700 troops based in Afghanistan as part of the NATO-led peacekeeping force. The soldiers were first deployed in 2002.