Rallies have been held around the world in support of Alan Johnston, the BBC journalist kidnapped in Gaza, to coincide with World Press Freedom Day.
The UN's Asha-Rose Migiro (c) said the abduction "served no cause"
Vigils were held by journalists in London, China and Indonesia to call for the release of Mr Johnston, who has been missing for more than seven weeks.
At a rally at the UN headquarters in New York, its deputy chief said the abduction "served no purpose".
Secretary General Ban Ki-moon, in Egypt, also called for his release.
In New York, UN Deputy Secretary-General Asha-Rose Migiro told about 100 gathered demonstrators: "No cause is served by Alan's captivity."
The UN officials and journalists - including BBC News World Editor Jon Williams and Martin Bashir from US TV network ABC News - held a minute's silence.
Many countries have joined the campaign for Alan Johnston
Mr Williams said: "Gaza is not an easy place to work... He stayed so long - and after so many colleagues had left - because he wanted to tell the story of Gaza to the world."
In the Indonesian capital, Jakarta, reporters, diplomats and human rights activists gathered in a park at dusk and lit candles in support of Mr Johnston's release.
A British embassy official read out a message from Mr Johnston's father, Graham.
"There is so much sympathy for our plight around the globe and we are overwhelmed at such support, all of which has helped to buoy us during these past seemingly interminable weeks," the letter said.
Journalists in Beijing also gathered at sunset to light candles and hold a minute's silence for Mr Johnston, who was seized after leaving his office in Gaza City on 12 March.
Mr Ban said he had been following "with dismay" the case of Mr Johnston, and again appealed for his immediate and safe release.
He widened the issue on World Press Freedom Day, saying: "Alarmingly, in seeking to shed light on the plight of others, journalists themselves become targets.
"This happens not just in the midst of armed conflict, but also in pursuit of stories on corruption, poverty and abuse of power."
Meanwhile, journalists protested against attacks and obstruction in their own countries.
The Media Alliance of Zimbabwe urged the government to scrap tough media laws, which it said led to "intimidation, harassment and unlawful arrests, detention and torture of journalists".
The Organisation for Security and Cooperation in Europe recalled the unsolved murder of three journalists in Serbia, saying the cases could "lead to self-censorship by journalists who fear the state is not able to protect them".
Robert Mahoney of the New York-based Committee to Protect Journalists said: "It used to be that a press pass was a passport to going into a country and a certain status, now a press pass is a liability."
He said most journalists killed on duty now are murdered, rather than caught in the cross-fire.