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Pyongyang has blamed its decision on South Korea joining a US-led initiative to search ships for nuclear weapons, calling it a "declaration of war".

"Any hostile act against our peaceful vessels, including search and seizure, will be considered an unpardonable infringement on our sovereignty," said a spokesman for the North's army.

"We will immediately respond with a powerful military strike."

"The Chinese firms that are moving are building infrastructure, they are building roads, they are providing jobs for people, but at the same time: what they are not doing, neither the Chinese government nor the companies, is raising any issues about how the population are being treated," Irene Khan, Amnesty International's secretary general, said today.

"Therefore we find that the Chinese presence is not helping the human rights situation. It might be aggravating it when revenues and resources are being paid into coffers of hugely corrupt and oppressive governments."

In an apparent reflection of Chinese anxiety over its reputation in Africa, both embassies and companies have been urged by Beijing to forge closer links to local communities.

China has also entered into a partnership with Britain's department for international development, (Dfid)intended to monitor and control the social and environmental impact of Chinese investment.

Shortly after Obama spoke, Dick Cheney gave a rebuttal at a conservative Washington think tank, the American Enterprise Institute. The former vice-president defended many of the Bush administration policies Obama is now unraveling, and mentioned either "September 11" or "9/11" 25 times.

Cheney said Saddam Hussein had "known ties" to terrorists, an apparent rehashing of the widely discredited Bush administration effort to link the Iraqi dictator to the September 11 2001 hijackers.

"After the most lethal and devastating terrorist attack ever, seven and a half years without a repeat is not a record to be rebuked and scorned, much less criminalised," Cheney said.

"In my long experience in Washington, few matters have inspired so much contrived indignation and phony moralising as the interrogation methods applied to a few captured terrorists."

Obama today said that indefinite detention at Guantánamo Bay and the prison's harsh interrogation methods had undermined the rule of law, alienated America from the rest of the world, served as a rallying cry and recruiting symbol for terrorists, risked the lives of American troops by making it less likely enemy combatants would surrender, and increased the likelihood American prisoners of war would be mistreated. The camp's existence discouraged US allies from cooperating in the fight against international terrorism, he said.

"There is also no question that Guantánamo set back the moral authority that is America's strongest currency in the world," he said. "Instead of building a durable framework for the struggle against al-Qaida that drew upon our deeply held values and traditions, our government was defending positions that undermined the rule of law."

He acknowledged that a number of Guantánamo prisoners could not be prosecuted yet posed a clear threat to the US: those who had trained at al-Qaida camps, commanded Taliban troops, pledged loyalty to Osama bin Laden and sworn to kill Americans.

"These are people who, in effect, remain at war with the United States," he said.

Obama defended his decision to release justice department memos detailing the Bush administration's legal rationale for waterboarding, sleep deprivation and other harsh interrogation techniques. He said those techniques had already been publicised and he had already banned them.

"In short, I released these memos because there was no overriding reason to protect them," he said. "And the ensuing debate has helped the American people better understand how these interrogation methods came to be authorised and used."

He defended his decision not to release photographs of US-held prisoners similar to those taken at the Abu Ghraib prison in Iraq. He said he feared they would inflame world opinion against the US and endanger US troops.

Today Medvedev joked with a group of students that the remote summit venue, 3,800 miles from Moscow or 5,300 miles via the epic Trans-Siberian Express, had been chosen to remind the Europeans of Russia's vast size. Several EU delegates moaned when Russia held last year's summit with the EU in western Siberia, Medvedev said.

"They complained: 'Oh, it's a long way.' We said: 'If you don't like it you can fly somewhere else.' They thought for a bit and said: 'OK, we're ready,'" Medvedev said. He added: "They [the Europeans] should understand how big Russia is and should feel its greatness. On the other hand, we also want a partnership with the EU. It's important for us to get together."

"Russia and EU relations are in stalemate. There is a serious lack of mutual understanding, a lack of willingness to understand each other, and a lack of strategic common values," Fyodor Lukyanov, editor-in-chief of Russia in Global Affairs, told the Guardian.

He went on: "Relations with Obama and the US are now better. At the same time relations with the EU are getting worse. Since the 1990s Russian-EU relations have been governed by the assumption that Russia would go the European way without applying for membership. This model is now exhausted. They need a new model."

Moscow has accused the 27-member bloc of creating new dividing lines in Europe by offering closer ties to six former Soviet republics.

The Eastern Partnership Initiative aims to forge close political and economic ties in exchange for democratic reforms.

Armenia, Azerbaijan, Belarus, Georgia, Moldova and Ukraine have signed up to the initiative, which seeks to bolster stability in the region.

However it does not offer the prospect of eventual EU membership.

On the divisive issue of energy supplies, President Medvedev raised questions about whether Ukraine can afford billions of dollars to top up its gas stocks.

"We have doubts about Ukraine's ability to pay," he said.

He also proposed that Moscow and the EU should help Ukraine get a loan for gas payments.

Russia supplies more than a quarter of EU gas needs. Its decision to cut all gas to Ukraine - a vital transit country - meant that many EU member states also lost their supplies of gas for two weeks in January.

Speaking in Khabarovsk, European Commission President Jose Manuel Barroso warned there should be no more disruptions to gas supplies from Russia.

Small outposts such as Amos Ester, which housed a few families, are periodically destroyed - but often rebuilt soon afterwards.

But correspondents say it is much rarer and more politically difficult for the government to evacuate larger ones.

Israel has also agreed to halt settlement activity, but has continued to build - mainly in settlement blocs on the west side of the West Bank barrier, areas Israel hopes to keep as part of an eventual peace deal.

Close to half a million Jewish settlers live in communities around the West Bank, some because they believe God gave the land to the Jewish people, others for lifestyle of economic reasons.

To perform their experiment, the researchers uploaded photos to each of the sites, then deleted them, but kept a note of direct URLs to the photos from the sites' content delivery networks.

When they checked 30 days later, these links continued to work for seven of the sites even though a typical user might think the photos had been removed.

Mr. Vick added that Tehran test-fired an even longer-range missile that used solid fuel, the Ashura, in late 2007 and several times afterward.

“They’re designing a whole family of solids to replace their liquids,” he said in an interview.

Mrs. Clinton was giving voice to a growing concern among administration officials, who have now had time to review the intelligence, that Iran seems to have made significant progress in at least two of the three technologies necessary to field an effective nuclear weapon.

The first is enriching uranium to weapons grade, now under way at the large nuclear complex at Natanz. The second is developing a missile capable of reaching Israel and parts of Western Europe, and now the country has several likely candidates. The third is designing a warhead that will fit on the missile.