The mothers of two US hikers held in Iran for nearly two years will renew a rolling hunger strike to protest their sons\' detention, they said in a statement Friday. Laura Fattal, 58 and Cindy Hickey, 50, were preparing to spend their birthdays without their sons for the second straight year in the coming days, and planned to fast from Saturday to next Thursday. \"The only thing we want for our birthdays is for justice to be served,\" said Fattal, whose son Josh, now 29, was arrested with Shane Bauer, 28, on July 31, 2009, near the border between northern Iraq and Iran. The pair are being held on charges of spying and entering Iran illegally. \"Iran knows that Josh and Shane are innocent, just as the whole world knows. I ask whoever is doing this to them -- and inflicting such pain on us and our families -- to have a heart and release them immediately.\" They will be joined by Ingrid Betancourt, a former Colombia hostage, and US anti-war activist Cindy Sheehan, whose son was killed fighting in Iraq. The hikers\' mothers, who first launched the rolling hunger strike on May 19, plan to hold a news conference in New York next Thursday. Iran has set a date of July 31 for the next hearing in the repeatedly delayed trial of the hikers, their lawyer told AFP on Monday. Washington has vehemently denied Tehran\'s charges and has pressed for their release. The hikers\' detention has added to tensions between the two countries over Iran\'s nuclear program and hardline stance towards Israel. Sarah Shourd, 32, arrested with the two men, is being tried in absentia after she returned to the United States when she was freed on humanitarian and medical grounds in September 2010, paying bail of around $500,000. Bauer and Fattal were allowed to call home in late May for just the third time since their arrest, and told their families they had staged a 17-day hunger strike earlier this year after being prevented from receiving letters.