VATICAN CITY (AP) -- Pope Francis laid out the priorities of his pontificate during his installation Mass on Tuesday, urging the princes, presidents, sheiks and thousands of ordinary people attending to protect the environment, the weakest and the poorest and to let tenderness "open up a horizon of hope."

It was a message Francis has hinted at in his first week as pontiff, when his gestures of simplicity often spoke louder than his words. But on a day when he had the world's economic, political and religious leadership sitting before him on the steps of St. Peter's Basilica for the official start of his papacy, Francis made his point clear.

"Please," he told them. "Let us be protectors of creation, protectors of God's plan inscribed in nature, protectors of one another and of the environment."

The Argentine native is the first pope from Latin America and the first named for the 13th-century friar St. Francis of Assisi, whose life's work was to care for nature, the poor and most disadvantaged.

The Vatican said between 150,000-200,000 people attended the Mass, held under bright blue skies after days of chilly rain and featuring flag-waving fans from around the world.

ASSAULT WEAPONS BAN WON'T BE IN DEMS' GUN BILL

WASHINGTON (AP) -- Senate Majority Leader Harry Reid has decided that a proposed assault weapons ban won't be part of a gun control bill the Senate plans to debate next month, the sponsor of the ban said Tuesday, a decision that means the ban stands little chance of survival.

Instead, Sen. Dianne Feinstein said she will be able to offer her ban on the military-style firearms as an amendment. Feinstein is all but certain to need 60 votes from the 100-member Senate to prevail, but she faces solid Republican opposition and likely defections from some moderate Democrats.

"I very much regret it," Feinstein, D-Calif., told reporters of Reid's decision. "I tried my best."

Asked about the decision, Reid, D-Nev., said he wanted to bring a gun bill to the full Senate that would have enough support to overcome any GOP attempts to prevent debate from even starting.

AP: COSTS OF US WARS LINGER FOR OVER 100 YEARS

OLYMPIA, Wash. (AP) -- If history is any judge, the U.S. government will be paying for the Iraq and Afghanistan wars for the next century as service members and their families grapple with the sacrifices of combat.

An Associated Press analysis of federal payment records found that the government is still making monthly payments to relatives of Civil War veterans - 148 years after the conflict ended.

At the 10 year anniversary of the start of the Iraq war, more than $40 billion a year are going to compensate veterans and survivors from the Spanish-American War from 1898, World War I and II, the Korean War, the Vietnam War, the two Iraq campaigns and the Afghanistan conflict. And those costs are rising rapidly.

U.S. Sen. Patty Murray said such expenses should remind the nation about war's long-lasting financial toll.

"When we decide to go to war, we have to consciously be also thinking about the cost," said Murray, D-Wash., adding that her WWII-veteran father's disability benefits helped feed their family.

Alan Simpson, a former Republican senator and veteran who co-chaired President Barack Obama's deficit committee in 2010, said government leaders working to limit the national debt should make sure that survivors of veterans need the money they are receiving.

MORTAR EXPLOSION IN NEV. KILLS 7 NC UNIT MARINES

HAWTHORNE, Nev. (AP) -- A mortar shell explosion killed seven Marines and injured a half-dozen more during a training exercise in Nevada's high desert, prompting the Pentagon to immediately halt the use of the weapon worldwide until an investigation can determine its safety, a military official said Tuesday.

The explosion occurred Monday night at the Hawthorne Army Depot, a facility used by troops heading overseas, during an exercise involving the 2nd Marine Expeditionary Force at Camp Lejeune, N.C. Several Marines from the unit were injured in the blast, authorities said.

It was not immediately clear whether the 60mm mortar shell exploded prematurely inside its firing tube or whether more than a single round exploded, the official said, speaking on condition of anonymity because the official wasn't authorized to speak about an ongoing investigation.

Eight men under the age of 30 were taken to Renown Regional Medical Center in Reno with injuries, such as penetrating trauma, fractures and vascular injuries. One of them died, five were in serious condition, one in fair condition and another was discharged, said spokesman Mark Earnest.

The identities of those killed won't be released until 24 hours after their families are notified.