Yves Heller, a spokesman for the International Red Cross, said that efforts were being made to ensure "a trip [to free the hostages] can be made as soon as possible".
"It's very important that there be a complete suspension of all military activity in the general area that we have submitted to the armed forces,'' he said.
Alvaro Uribe, the Colombian president, has acknowledged that military jets had flown over the jungle clearing where Farc freed three policemen and a soldier on Sunday, the Associated Press reported.
His government issued a statement on Monday vowing to suspend all air force activity in the affected areas during this week's planned release of two other hostages, the report said.
The release of Jara, who has been held for almost eight years, had been thrown into doubt this week when Uribe suspended the involvement of Piedad Cordoba, a senator previously involved in negotiation efforts.
Farc has fought the Colombian government for decades in what it says is battle on behalf of the country's poor.
However, the group has been weakened considerably in recent years by a sustained Colombian military effort supported by $4bn from the US for sophisticated surveillance, communications intercepts, and other tools.
It has also been battered by the deaths of several senior commanders, desertions due to low morale, and the rescue in July of a group of captives it had hoped to use as bargaining chips, including Ingrid Betancourt, the French-Colombian politician, and three US contractors.