"We're throwing down a red flag and saying, if this is true, please stop it," Eckhard said.
British Prime Minister Tony Blair did not refute Short's claims but called them "irresponsible." He told a press briefing that British intelligence agents act in accordance with international and domestic laws.
"I am not going to comment on [security services'] operations -- not directly, not indirectly. That should not be taken, as I say, as any indication about the truth of any particular allegations and I think the fact that those allegations were made, I think, is deeply irresponsible," Blair said.
Eckhard said Britain's UN ambassador, Emyr Jones Parry, who is in London, called Annan on Blair's behalf to discuss the matter. He did not give details.
"Whether or not this is widespread, we don't know. Whether or not this happened, this specific incident happened, we don't know. But we will take whatever measures we can to protect the confidentiality of the secretary-general's phone conversations," Eckhard said.
Eckhard said such protective actions include securing phones and fax lines and checking the secretary-general's office for electronic bugging devices. He said the UN is not equipped to prosecute any cases of spying, if proven, but stressed such activity is not allowed under international law.
He cited three treaties -- in particular, a section of the 1946 Convention on the Privileges and Immunities of the United Nations spelling out that UN premises "shall be immune from search, requisition, confiscation, expropriation and any other form of interference."
Short's charge came a day after British authorities dropped their prosecution against a British intelligence agency worker who admitted leaking a document that disclosed a U.S. appeal for British help to monitor the phones and e-mails of UN Security Council members ahead of the Iraq war. The members allegedly targeted included temporary members Pakistan, Chile, Cameroon, Angola, and Guinea, who were undecided on whether to support military action against Iraq.
In addition, Mexico's ambassador at the time, Adolfo Zinser, said that the United States had advance information about an initiative he was going to submit to the Security Council. Mexico sent a letter in December 2003 asking the United States and Britain to explain the accusations of spying on UN delegations.
U.S. officials have refused to comment on the accusations.
The latest developments prompted humorous reactions by at least two Security Council ambassadors. Russian Ambassador Sergei Lavrov said that, if true, the allegations showed that British intelligence services, "at least technically, are very professional."
Lavrov also denied any similar such activity by Russia.
"I don't think you could find any, even [a] suspicion, that the secretary-general's office was bugged by the Russian intelligence service. But all this, as I said, needs to be investigated [by] UN security, of course," Lavrov said.
Spain's UN ambassador, Inocencio Arias, told reporters: "Everybody spies on everybody."