In a sudden announcement that caught Catholics around the world off guard, Pope Benedict XVI said he will resign at the end of February, becoming the first pontiff to step down in nearly 600 years.

The 85-year-old pontiff made the announcement Monday, saying he no longer had the strength to carry out his papal duties.

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry," the pope said according to a statement released by the Vatican.

"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry."
- Pope Benedict XVI

He said he is aware of the "seriousness" of his resignation, but that he did so in "full freedom." He will live out his days on Vatican grounds, according to officials.

The last pope to resign was Pope Gregory XII, who stepped down in 1415 in a deal to end the Great Western Schism among competing papal claimants. The sudden announcement sets the stage for the Vatican to hold a conclave to elect a new pope by mid-March, since the traditional mourning time that would follow the death of a pope doesn't have to be observed.

There are several papal contenders in the wings, but no obvious front-runner, according to Vatican watchers.

A Vatican spokesperson told "Fox & Friends" that Pope Benedict "will not take part in conclave" to choose his successor. Officials hope to have a new pope in place in time for the start of Holy Week, on March 14. Although there has been much speculation about Pope Benedict's health, a Vatican spokesman said he is not in any immediate danger.

"There's nothing immediately serious or grave," the Vatican spokesman told ABC.

The pope's 89-year-old brother, Georg Ratzinger, told a German news agency that the pope has had difficulty walking recently and has considered stepping down for months.

“His age is weighing on him,” Georg Ratzinger said. “At this age my brother wants more rest.”

Born Joseph Aloisius Ratzinger, Pope Benedict became the 265th pope after being elected by his fellow cardinals on April 19, 2005, at the age of 78 following the death of the popular John Paul II. The ninth German pope and first in nearly 500 years, Benedict was ordained in 1951 and was a major figure at the Vatican stage for decades before his ascension.

Ratzinger chose the name Benedict, which comes from the Latin word meaning "the blessed," in homage to Pope Benedict XV, who was pope during World War I, and Saint Benedict of Nursia, who established the Benedictine monasteries.

During his papacy and in the years prior, Benedict was a key figure in the church's efforts to address widespread instances of sexual abuse of children by priests. In 2001, then-Cardinal Ratzinger convinced John Paul II to put the Congregation for the Doctrine of the Faith, which he led, in charge of investigating cases and setting policy regarding what he termed "filth" in the church.

As a cardinal, Ratzinger pushed through important reforms, including making Internet offenses against children a violation covered by canon law, extending child abuse offenses to include the sexual abuse of all under 18, waiving of the statute of limitation and speeding the process of dismissing guilty priests.

Even before becoming pope, Ratzinger had experienced health problems and attempted to resign from his role as prefect of the Congregation for the Doctrine of Faith several times, only to stay on at the behest of Pope John Paul II. In 1991, Ratzinger suffered a stroke, according to reports.

After becoming pope, Benedict, who predicted a short tenure for himself, suffered another stroke in May 2005, according to the Vatican. He is also believed to suffer from a heart condition.

As pope, Benedict embraced technology. In December, he began using Twitter, wher
e he has 1.5 million followers.

"We must trust in the mighty power of God’s mercy," read his most recent tweet, posted yesterday. "We are all sinners, but His grace transforms us and makes us new."

The Associated Press contributed to this report.