A row over the detention and deportation of World Council of Churches (WCC) delegates to a climate change conference in Israel and the Palestinian Territories shows little sign of cooling down.

Several WCC staff and other representatives were detained earlier this month by security staff at Israel's Ben Gurion airport in conditions the WCC described as "intolerable" before being deported. It said in a statement: "Others were ultimately admitted to Israel after exceptionally long and confrontational interrogation. All reported aggressive, accusatory and abusive questioning, threats and intimidation above and beyond what the WCC is prepared to consider tolerable."

The WCC and its general secretary Rev Dr Olav Fykse Tveit used exceptionally strong language to characterise Israel's actions, describing them as "deeply regrettable" and calling for an apology.

The Israeli Embassy subsequently contacted Christian Today accusing delegates to the conference of not answering questions "in a truthful manner" and alleging they "attempted to mislead Israeli border authorities regarding the purpose of their visit". It said: "We believe they were instructed to so behave by the WCC, in a manner that is irresponsible, endangers the public safety, and needlessly raises suspicion."

It stressed the need to maintain border security and said: "Israeli authorities were not at fault and did not act overzealously. We believe it is the WCC which needs to explain its highly irregular behaviour."

However, the WCC has strongly denied wrongdoing. Following a meeting last week with the Israeli Mission in Geneva, where it is based, it issued a statement reiterating its objection to the "intimidating and traumatic" experience of its delegates.

"At the airport, some travelers were interrogated repeatedly for up to eight hours and accused of lying," it said. "They said Israeli officials accused them of arriving for an entirely different reason than for their stated purpose: a meeting on climate change hosted by member churches in the region. They were threatened with a 10-year ban on entry to Israel and with being listed on Interpol watch lists; and they were detained in prison-like conditions for up to three nights before being deported. The treatment of these travelers is unwarranted and unacceptable."

Speaking to Christian Today, Tveit said he believed delegates had answered questions truthfully at the airport. However, he said that 10-year-old guidance to WCC visitors to Israel might have led to a misunderstanding by Israeli authorities. It stressed that visitors should always answer questions truthfully, but advised them not to volunteer information as it could lead to confusion. Tveit said the guidance would be rewritten.

At the meeting in Geneva, he said: "We also emphasised that there was no illegal activity by WCC participants at any time. There was no intention to do anything illegal or immoral."

However, he added: "Even if there was some misunderstanding here, it didn't warrant this sort of reaction, with them being accused of lying."

A further question is why the WCC delegates to the Israel conference were singled out for such treatment. Tveit said of those held at Ben Gurion airport: "When they said they were representing the WCC that caused a kind of alarm and that's when the interrogation started. They were even told by some of these interrogators that the WCC was a very bad organisation, it was almost described as an illegal or criminal organisation."

However he said he had been told by the Israelis at the meeting in Geneva that the WCC had not been "blacklisted" by Israel and that the state of Israel had no issue with the WCC as such. "They know we make critical statements on the Palestinian issue about obstacles to peace; that is part of our witness," he said. "However, their message was that there is no connection between our position in that sense and what happened at the border control. Whether that is the reality in the end we will have to see."