A former US spy agency contractor facing charges of espionage remains in hiding at a Moscow airport for a fifth day, while US politicians issue strong warnings to cut ties if Ecuador takes him in.

Robert Menendez, the chairman of the US Senate Foreign Relations Committee said on Wednesday, that he would seek to end the preferential treatment for Ecuadorean goods if the South American nation offers political asylum to Edward Snowden.

Menendez said he would lead the effort to prevent the renewal of Ecuador's duty-free access to US markets under the Generalized System of Preferences program, and also to block the renewal of the Andean Trade Promotion and Drug Eradication Act, both of which expires at the end of next month.

Ecuador exported $5.4 billion worth of oil, $166m of cut flowers, $122m of fruits and vegetables and $80m of tuna to the US under the Andean trade program in 2012.

Ecuador said a decision could take weeks and asked Washington to argue its case for extradition.

Snowden remains in the transit area of Moscow's Sheremetyevo airport and is seeking safe passage to Ecuador.

Extradition order

Hong Kong said the US request to arrest him did not fully comply with its legal requirements.

But White House spokesman Jay Carney lashed out at Beijing, saying its failure to "honour extradition obligations" had dealt a "serious setback" to efforts to build trust with new President Xi Jinping.

Russian Foreign Minister Sergei Lavrov repeated Putin's stated opinion that he should choose a destination and fly out as soon as possible, state-run Itar-Tass news agency reported.

But Ecuador's foreign minister indicated a decision on Snowden's asylum request could take upto two months.

"It took us two months to make a decision on Assange so do not expect us to make a decision sooner this time," Foreign Minister Richard Patino said in Kuala Lumpur, referring to the founder of anti-secrecy group Wikileaks, Julian Assange.

Asylum offer from Venezuela

Venezuela's President Nicolas Maduro said on Wednesday he would "almost certainly" grant political asylum to Snowden.

"If he asked us for it, we would think about it and we would almost certainly give it to him, because political asylum is an international human rights institution to protect the persecuted," said Maduro.

Snowden fled to Hong Kong after leaking details of secret US government surveillance programmes, then flew on to Moscow on Sunday. There was no sign on Wednesday of him registering for onward flights out of Russia.

"They are not flying today and not over the next three days," an Aeroflot representative at the transfer desk at Sheremetyevo said when asked whether Snowden and his legal adviser, Sarah Harrison, were due to fly out.

"They are not in the system."