By Daniel Burke, CNN Belief Blog Co-Editor

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(CNN) - As President Obama rallies support for a military strike on Syria, Pope Francis condemned chemical weapons and called for an international day of fasting and prayer to press for a peaceful resolution to Syria's escalating civil war.

The pope tweeted an anti-war message to his nearly 3 million Twitter followers on Monday, repeating a theme he has sounded with increasing urgency in recent days.

War never again! Never again war! — Pope Francis (@Pontifex) September 2, 2013

On Sunday, Francis devoted much of his Angelus address in Rome to Syria.

"There are so many conflicts in this world which cause me great suffering and worry," the pope said, "but in these days my heart is deeply wounded in particular by what is happening in Syria and anguished by the dramatic developments which are looming."

However, the pope also said that people who use chemical weapons - as the Syrian government has been accused of doing - will face divine judgement.

"With utmost firmness I condemn the use of chemical weapons: I tell you that those terrible images from recent days are burned into my mind and heart. There is a judgment of God and of history upon our actions which are inescapable!"

The pope also proclaimed September 7 a day of prayer and fasting for Syrian peace, and invited the world's 1.5 billion Catholics, as well as other Christians, followers of different religions and "all men of goodwill" to join him.

From 7-12 p.m. in Rome, Francis said, "we will gather in prayer and in a spirit of penance, invoking God’s great gift of peace upon the beloved nation of Syria and upon each situation of conflict and violence around the world."

"Humanity needs to see these gestures of peace and to hear words of hope and peace!" he said.

On Monday, the pope met with a delegation from the World Jewish Congress as Judaism's High Holidays approach. Rosh Hashanah, the Jewish new year, begins September 5.

“Pope Francis’ leadership has not only reinvigorated the Catholic Church but also given a new momentum to relations with Judaism," said WJC President Ronald S. Lauder.

"Never in the past 2,000 years have relations between the Catholic Church and the Jewish people been so good."