Palestinian Authority Chairman Mahmoud Abbas has told the British Broadcasting Corp. he has "credible evidence" a BBC journalist kidnapped a month ago in the Gaza Strip was "safe and well," the network's top executive said Thursday. Alan Johnston, a native of Scotland, was abducted at gunpoint in Gaza City on March 12. There has been no sign of life from him since, and no word from his captors. No other foreigner has been held in Gaza as long. BBC director general Mark Thompson appealed for Johnston's release at a news conference in the West Bank town of Ramallah. At a meeting with Abbas on Wednesday, "he told me that he had credible evidence that Alan was safe and well," Thompson said. Thompson said there have been no contacts with Johnston's captors, and no demands from them. "It is vital for all journalists to be able to report freely and without fear of harassment and intimidation," he told the news conference. "I appeal to all those who may have influence with the kidnappers to use their best endeavors to secure Alan's release, safely and speedily, and to ensure his return to his family and friends as quickly as possible," he said. Thompson said he did not know why the case was taking so long to be resolved. More than a dozen foreign journalists and aid workers have been abducted by Gaza gunmen in the past 18 months, often in a bid to wrest money or jobs. Most have been released unharmed within hours or days. The one exception was the abduction of two Fox News employees in August, which lasted two weeks before they were freed, unharmed. Abbas confidant Saeb Erekat said the Palestinian president "has been reassured by many sources that Mr. Johnston is alive." Abbas, he added, "is doing his best" to obtain Johnston's release. "I feel ashamed of this despicable act," he told Sky News. "We condemn it with the strongest possible terms." Thompson's appeal for Johnston's release was part of a daylong calendar of international events meant to dramatize the abducted journalist's plight, including a statement from his parents at a London news conference. "You have families. Please think about what this is doing to my family, including in particular the distress and deep, deep concern Alan's mother and sister have had to endure for all these long weeks," Johnston's father, Graham Johston, appealed to his son's abductors. "As I have said before - please - let my son go. Now. Today!" he said. In Gaza, about 200 Palestinian journalists held a rally simultaneously with the news conference in Ramallah, hoisting posters reading, "Free Alan" and "Alan, they are not one of us," referring to the kidnappers. "We are disappointed by presidential and governmental footdragging on the release of our kidnapped colleague, said Sakher Abu-Owan, a Palestinian journalist. "Our concern over Alan's safety is growing every day." The journalists then drove through the streets of Gaza City in cars plastered with posters of Johnston.