North Korean leader Kim Jong Un threatened to launch a powerful retaliatory strike against South Korea if provoked, state media said Sunday, a day before the start of annual South Korean-U.S. military drills that Pyongyang calls an invasion rehearsal.

South Korean and U.S. officials have said that the 12-day, largely computer-simulated war games set to start Monday are defensive in nature.

A strong earthquake measuring 6.8 shook southwestern Siberia in Russia on Sunday but caused no casualties or serious damage, the Russian emergencies ministry said.

The quake's epicenter was recorded at 1:20 pm local time (0620 GMT) in the republic of Tuva about 107 kilometers (66 miles) from the town of Kyzyl, which saw tremors of a similar magnitude on December 27.

Pakistani security forces on Saturday began demolishing the compound where Osama bin Laden was killed in a covert U.S. raid last May in the garrison town of Abbottabad, police and witnesses said.

"Two bulldozers are engaged, the demolition work is in progress, it is being done by security forces, including troops," a police official on the spot told Agence France Presse by telephone.

A shallow 5.9-magnitude earthquake sent panicked people fleeing onto the streets in Taiwan's second-largest city of Kaohsiung on Sunday as rail services were temporarily suspended.

The quake struck 57 kilometers (35 miles) east of the city at 10:34 am (0234 GMT) at a depth of just four kilometers, the U.S. Geological Survey said.

Fifteen tourists were killed and another 19 injured when their bus plunged into a ravine, Chinese authorities said -- the latest deadly accident on the nation's dangerous roads.

The incident happened on Saturday morning after the bus took a bend on a highway in Shanxi province, the government of Jincheng city -- where the accident took place -- said in a statement.

The engineer operating the Argentine train that crashed this week killing 51 passengers blamed the brakes for failing, after he repeatedly warned they were faulty, a judicial source said Saturday.

The engineer, Marcos Cordoba, is being investigated by police but was free after being treated at a hospital.

Africa's top envoy on Saturday offered a political solution to prevent chaos in Senegal by suggesting that President Abdoulaye Wade retire after two years if he wins Sunday polls.

Former Nigerian President Olusegun Obasanjo said his proposal was a way to "bridge the gap" between government and the opposition as a standoff over Wade's bid for a third term led to violent protests in the country.

A U.N. atomic watchdog's report saying that Iran has substantially boosted uranium enrichment is "added proof" that Tehran is trying to obtain nuclear weapons, Israel said on Saturday.

"The report by the International Atomic Energy Agency gives added proof that Israeli beliefs are true" about Iran's nuclear program, a statement from Prime Minister Benjamin Netanyahu's office said.

A U.S. drone crashed in northwest Pakistan's tribal district near the Afghan border late Saturday, officials said.

The unmanned reconnaissance aircraft came down in the mountainous Machikhel area about 30 kilometers east of Miranshah, the main town in North Waziristan region, which is frequently targeted by drone strikes against Taliban and al-Qaida militants, military and security officials said.

Two police officers from the African Union-United Nations peacekeeping mission to Sudan's Darfur region (UNAMID) have been shot and wounded by unidentified gunmen, the mission said on Saturday.

They both received leg wounds and were being treated at a UNAMID hospital, said Christopher Cycmanick, a spokesman for the mission.