The sudden closure of many American diplomatic missions in North Africa and Middle East were prompted after the US intercepted conversations between two senior al-Qaeda leaders.
The chatter, involving top leader Ayman al-Zawahiri, represented one of the most serious plots since the 9/11 attacks, the New York Times wrote.
The US earlier said the closures in North Africa and the Middle East were “out of an abundance of caution”.
Some 20 US embassies and consulates were shut on Sunday.
A state department global travel alert, issued last week, is also in force until the end of August.
US diplomatic posts in Abu Dhabi, Amman, Cairo, Riyadh, Dhahran, Jeddah, Doha, Dubai, Kuwait, Manama, Muscat, Sanaa and Tripoli will remain closed until Saturday.
Several European countries have also temporarily shut missions in Yemen and the UK Foreign Office is advising against all travel to the country.
Both the White House and the US state department said the threat came from al-Qaeda in the Arabian Peninsula (AQAP), but refused to divulge further details.
Some 20 US embassies and consulates in North Africa and Middle East were shut
But according to the New York Times, the US intercepted communications between Ayman al-Zawahiri and the group’s head in Yemen, Nasser al-Wuhayshi.
The paper said that no targets had been singled out in the discussions, but that a possible attack appeared to be imminent.
A US official told the Associated Press news agency that Ayman al-Zawahiri’s message had been picked up several weeks ago and appeared initially targeted at Yemen.
US lawmakers have said it was a huge plot in the final stages, but have offered no specifics.
On Monday, a top member of the House intelligence committee Dutch Ruppersberger told CNN the warnings were not designed to frighten Americans, though he said a planned attack could be “anywhere”.
“Americans should live their lives… we just want them to be aware,” Representative Dutch Ruppersberger said.
White House spokesman Jay Carney said he could not be “specific” about the threats.
He said: “Our current information suggests that al-Qaeda and affiliated organizations continue to plan terrorist attacks both in the region and beyond. And our information suggests that they may focus efforts to conduct attacks in the period between now and the end of August.”
Meanwhile, officials in Yemen have released the names of 25 al-Qaeda suspects, saying they had been planning attacks targeting “foreign offices and organizations and Yemeni installations” in the capital of Sanaa and other cities across the country.
There was also increased security at government buildings and checkpoints in Yemen on Monday.
AQAP, the Yemeni branch of al-Qaeda, has also been blamed for the foiled Christmas Day 2009 effort to bomb an airliner over Detroit and explosives-laden parcels that were intercepted the following year aboard cargo flights.
Seven suspected al-Qaeda militants were killed in two US drone air strikes in southern Yemen in June, officials say.
North Korea has asked foreign embassies in Pyongyang that might wish to get staff out if there is a war to submit plans to it by April 10, Reuters agency has reported.
Initial reports by Russia’s Foreign Ministry and China’s Xinhua news agency suggested that North Korea had suggested that embassies should consider closing because of the risk of conflict.
The request came amid a military buildup by the US in South Korea following North Korea’s warnings that war was inevitable.
“We believe they have taken this step as part of their continuing rhetoric that the U.S. poses a threat to them,” Britain’s Foreign Office said in a statement after the reports from Russia and China.
North Korea has asked foreign embassies in Pyongyang that might wish to get staff out if there is a war to submit plans to it by April 10
A British diplomatic official, who spoke on condition of anonymity, said that European Union embassies in Pyongyang had been summoned to deliver their evacuation plans.
Under the Vienna Convention that governs diplomatic missions, host governments are required to facilitate the exit of embassy staff in the event of conflict.
Russia’s Foreign Ministry said earlier that North Korea had “proposed that the Russian side consider the evacuation of employees in the increasingly tense situation”, according to Denis Samsonov, a spokesman for its embassy in Pyongyang.
A report from Chinese state news agency Xinhua chimed with the Russian report, saying that Pyongyang had asked embassies to consider evacuation if the situation deteriorated.
North Korea, ruled by 30-year old Kim Jong-un, has not issued any statement indicating which of the conflicting reports was true. (Reuters)
Ecuadorean President Rafael Correa has said the UK would be committing diplomatic suicide if it tried to enter his country’s embassy in London.
Rafael Correa said such a move would open up the UK to having its diplomatic missions around the world entered.
The president was speaking to state television about the continuing dispute over WikiLeaks founder Julian Assange.
Julian Assange has been in the embassy since June and been granted asylum by Ecuador as he fights extradition.
The UK says it is obliged to extradite Julian Assange to Sweden, where he faces questioning over sex assault claims, which he denies, and he will be arrested if he leaves the embassy.
Ecuadorean President Rafael Correa has said the UK would be committing diplomatic suicide if it tried to enter his country's embassy in London
Julian Assange entered the embassy in June while on bail before extradition proceedings against him started.
The interview with Rafael Correa opened with a short report from inside the Ecuadorean embassy in London.
It showed Julian Assange hugging his lawyer, the former Spanish judge Baltasar Garzon, just minutes before he addressed crowds of his supporters from the embassy’s balcony on Sunday.
Rafael Correa was then asked if he thought there was now no possibility the UK authorities would enter the embassy premises to arrest Julian Assange, as they had previously indicated they might in a letter to Ecuadorean officials.
The preseident said: “While the United Kingdom hasn’t retracted nor apologized, the danger still exists.”
He said such a course of action would be “suicide for Great Britain because then people could enter their diplomatic premises all around the world and they wouldn’t be able to say a thing”.
There was very little said on what the next diplomatic step might be regarding removing Julian Assange from the embassy.
But Rafael Correa said, if needed, he was prepared to take the issue to the United Nations.
He also said Ecuador was hoping for strong support from a meeting of the Organization of American States on Friday.
“Remember that David beat Goliath. And with many Davids it’s easier to bring down a number of Goliaths,” he said.
“So we’re hoping for clear and coherent backing because this violates all inter-American law, all international law, the Vienna Convention and all diplomatic traditions of the last, at least, 300 years on a global scale.”
Returning to the question of Julian Assange, Rafael Correa said: “The British say they have no choice but to extradite him but why didn’t they extradite Augusto Pinochet?”
While Rafael Correa may not have thrown any fresh light on where the stalemate goes next, he did reiterate that the channels of negotiation with the UK were still open.
The UK has insisted it will not grant Julian Assange “safe passage” to Ecuador as it seeks a diplomatic solution to him being given asylum.
The Supreme Court in May dismissed Julian Assange’s bid to reopen his appeal against extradition and gave him a two-week grace period before extradition proceedings could start.
On Sunday, Julian Assange, 41, used his first public statement since entering the embassy to claim asylum – delivered from a balcony – to call on the US to stop its “war on whistle-blowers”.
The US is carrying out an investigation into WikiLeaks, which has published a mass of leaked diplomatic cables, embarrassing several governments and international businesses.
In 2010, two female ex-WikiLeaks volunteers accused Julian Assange, an Australian citizen, of committing sexual offences against them while he was in Stockholm to give a lecture.
Julian Assange claims the sex was consensual and the allegations are politically motivated and fears extradition to the US if extradited to Sweden.