New York - Lady Gaga and Ariana Grande urged US leaders on Monday to act to tighten gun laws following the carnage in Las Vegas, as artists voiced shock at the deadliest shooting in modern US history.While most artists left their comments to general messages of sympathy after the assault on a country music festival, Gaga used her social media power to press politicians."This is terrorism plain and simple. Terror bares (sic) no race, gender or religion. Democrats & Republicans please unite now," the pop star wrote to more than 71 million followers on Twitter, where her account is the seventh most popular.She took to task the call for prayers by House Speaker Paul Ryan, who like President Donald Trump and most other Republican leaders is a staunch opponent of regulations on guns."Prayers are important but @SpeakerRyan @realDonaldTrump blood is on the hands of those who have power to legislate. #GunControl act quickly," she wrote.Gaga also invited fans to join her in a live-streamed 20 minutes of silent meditation or prayer "to connect us all through inner peace".Grande - whose own concert in Manchester was attacked in May by a supporter of the Islamic State group, killing 22 people - indicated that she saw little distinction with the assault in Las Vegas, where the gunman's motivations were not immediately clear."My heart is breaking for Las Vegas. We need love, unity, peace, gun control & for people to look at this & call this what it is = terrorism," Grande tweeted.Change of heart from country artist At least 59 people were killed and 500 were injured when a heavily armed gunman opened fire from his hotel room onto an open-air country music festival on the Las Vegas Strip.The bloodbath changed the views of one artist present - Caleb Keeter, the guitarist for the Texas-based Josh Abbott Band.A longtime supporter of gun rights, he said that members of his crew had legal firearms - which were useless in the chaos as bullets rained down."We need gun control. RIGHT. NOW," he tweeted."My biggest regret is that I stubbornly didn't realize it until my brothers on the road and myself were threatened by it," he wrote.Jason Aldean, who was playing the headlining set, called the attack "beyond horrific"."It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night," he wrote on Instagram.