Around 1,000 Pakistani paramilitary troops backed by helicopters are battling separatists in the country's restive southwest, with the rebel death toll rising to 13 Thursday on the second day of fighting.

The clash with separatists began on Wednesday in the area of a gasfield in Pirkoh, some 245 kilometers (152 miles) southeast of Quetta, the capital of Baluchistan province which is wracked by a tribal insurgency, Taliban attacks and sectarian violence.

A Mexican gang member was executed Wednesday night in Texas for strangling to death a woman who refused to pay a tax on her illegal drug sales.

The lethal injection of Manuel Vasquez, 46, left Texas prison officials with only enough pentobarbital to execute one more prisoner, scheduled for March 18 in the most active death penalty state.

Much of Syria is regularly plunged into debilitating darkness, experts said Wednesday, highlighting the scale of the war's devastation as the conflict enters its fifth year.

Analyzing satellite images, scientists from Wuhan University in China found that since March 2011, when the war broke out, "the number of lights visible over Syria at night has fallen by 83 percent," a coalition of 130 non-governmental organizations said in a statement.

Two police officers shot overnight in the troubled Missouri city of Ferguson -- which for months has battled racial tensions -- were victims of an "ambush," police said Thursday.

One officer was shot in the face, and the other in the shoulder, as protesters outside the Ferguson police station -- who gathered after the city's embattled police chief resigned -- dispersed at around midnight (0500 GMT).

The presence of Iranian advisers in the Iraq battle for Tikrit is "concerning" to the United States, Secretary of Defense Ashton Carter said Wednesday.

A mostly Shiite Iraqi force, including Iranian-backed militias, entered Tikrit Wednesday from the Islamic State group after a 10-day push to enter the city.

The United States will deliver Humvees and drones to Ukraine and hit rebel leaders and their alleged supporters in Russia with further sanctions, after repeated ceasefire violations, officials said Wednesday.

More than $75 million worth of "non-lethal defensive" equipment will be sent to Kiev, a senior administration official said.

U.S. Secretary of State John Kerry urged lawmakers Wednesday to give President Barack Obama new war powers to strike against Islamic jihadists at "a pivotal hour" in the battle against the militants.

But senators pressed Kerry, Defense Secretary Ashton Carter and top U.S. military officer Martin Dempsey on whether a new resolution would lead to "mission creep" that could see hundreds of U.S. ground troops sent back into the Middle East.

Seven U.S. Marines and four aircrew were feared dead Wednesday after an army helicopter crashed during a night training exercise in Florida, military officials said.

The UH-60 Black Hawk helicopter was reported missing Tuesday around 8:30 pm (0030 GMT Wednesday) near Eglin Air Force Base. The area was under heavy fog.

Recent satellite imagery shows no sign of North Korea preparing an imminent nuclear test, despite a rise in military tensions on the Korean peninsula, a U.S. think-tank said Wednesday.

North Korea has ramped up the volume on its bellicose rhetoric in recent weeks in response to the launch of annual South Korean-U.S. joint military exercises.

The Ferguson city manager left his post Tuesday after a scathing U.S. Justice Department report found a culture of racism in the St. Louis suburb's police department and municipal offices.

Ferguson, in Missouri, sprang to international prominence in August when a white policeman shot dead an unarmed black teenager, provoking sometimes violent protests and soul-searching in the United States.