Three explosions went off as the Dortmund team made their way to their Signal Iduna Park stadium for the Champions League quarter-final first leg against Monaco on Tuesday.
Guardiola was shocked by the incident in Germany which caused the tie to be postponed for 24 hours and left Dortmund defender Marc Bartra needing surgery to a broken wrist.
The German Federal Prosecutor's Office said three letters claiming responsibility found near the site of the attack made Islamic extremists the possible perpetrators.
"It's a bit scary how the world is. It's going a bit crazy," Guardiola told reporters on Thursday.
"What's happening in Syria... hopefully the president of the United States, the presidents of Russia and China, can intervene and find a solution, because if not we don't know where we'll end up.
"We have to keep living without fear, but these things can happen.
"I hope Marc has a fantastic recovery. In terms of what happened, it was scary and it was serious, but he lived to tell the tale.
"But we're in a world where we don't know where we'll end up, that's the truth. I don't know where we're heading."
Meanwhile, on footballing matters, Guardiola has confirmed that he currently does not have a first choice goalkeeper and will platoon Claudio Bravo, who turned 34 on Thursday, and Willy Caballero on a game-by-game basis.
Bravo has struggled through a disappointing debut season with City having arrived at the club as apparent successor to England international Joe Hart, who was sent on loan to Torino.
Back-up Caballero appeared to have displaced Bravo as City's first choice but Guardiola insisted that is not the case.
"Last week I decided for Claudio. Saturday I am going to decide," Guardiola said.
"It depends on if the opponent makes a lot of high pressing or not. The way the opponent plays as well.
"What I see in the training session. I have confidence with both. We will see.
"It's my decision. I like both to be involved."
Guardiola also insists that injury-plagued defender Vincent Kompany has a future to play with his club, not least because City's club captain is still under contract next season.
The Belgian came through 90 minutes in last week's 2-1 defeat at leaders Chelsea, his first complete game in the league this season, only to miss out on the weekend win over Hull through a minor injury.
"Yes, he has a contract," said Guardiola when asked if Kompany figures in his plans for next season.
"He can hopefully play two games a week in the next period, in the future. He can do that.
"But after the game against Chelsea he reacted to that, had problems with the leg, and we didn't want to take a risk.
"But of course the good news was he could play 90 minutes, a tough game at Stamford Bridge and he played at a high level.
"What we have seen these two or three days, he's ready for the next game."