The Venezuelan opposition leader Juan Guaidó has directly urged the west to keep up the pressure to bring about elections in his country within four weeks, the UK foreign secretary has said.

Jeremy Hunt spoke with Guaidó by phone on Wednesday before an informal meeting of EU foreign ministers in Romania on Thursday that will discuss what further economic sanctions can be imposed on senior figures in the Venezuelan leadership.

Key EU countries are prepared to recognise Guaidó as the legitimate interim president of Venezuela if Nicolás Maduro refuses to call fresh elections by Sunday.

Guaidó, 35, a former student leader and head of Venezuela’s opposition-run national assembly, has been at the forefront of a renewed attempt to force Maduro from power.

He said in an opinion piece for the New York Times on Wednesday that he had held “clandestine” meetings with the military to try to persuade them to withdraw their support for Maduro. Protesters marched in Caracas on Wednesday calling for Maduro to stand down.

The European parliament has voted to recognise Guaidó due to his role as president of the national assembly. But not every EU state has issued the Sunday ultimatum, and Russia is looking to see if these divisions can be prised open.

Moscow has so far offered full-throated support for Maduro. It is estimated to have invested £13bn in Venezuela through refinancing of the country’s debt and through oil and arms deals.

Although the bulk of the anti-Maduro sanctions policy is being determined in Washington and Latin America, the EU could have a role in trying to cut off supplies to Maduro. Spain, the leading EU country in the crisis, opposes military intervention.

Maduro has accused Donald Trump and a “group of extremists around him” of plotting to topple him in order to seize Venezuela’s oil, and said he risked transforming the country into a new Vietnam.

Venezuela’s supreme court has imposed a travel ban and financial restrictions on Guaidó, including freezing his bank accounts.

Speaking on BBC radio, Hunt said a humanitarian catastrophe was unfolding in the country, with citizens struggling to find scraps of food.

“Here in Britain and Europe we cannot determine the outcome of what happens in Venezuela. It has to be for the people of Venezuela,” he said.

“But what we can do is support the president of the national assembly that wants to uphold the constitution and is saying there need to be elections in four weeks because there is not a legitimate president.”

He added: “We are not considering sanctions against the whole country because there is a humanitarian situation and we wouldn’t want to make the situation even worse. But targeted sanctions against the kleptocrats who have enriched themselves on the back of the rest of the population who are very poor, that is something I think can be effective.”

He said a decision on sanctions is not expected immediately on Thursday.

Hunt, a Conservative, said “this is not an ideological crusade”, pointing out that Guaidó was a member of Socialist International.

“I doubt if he agrees with President Trump on very many policies at all and that is why it is rather extraordinary Maduro continues to get such strong support from Jeremy Corbyn and John McDonnell,” he said.

“Simply because they share Maduro’s anti-western world view is not a reason to turn a blind eye to someone who has driven his people into poverty where 70% of the population is facing malnutrition.”

The Labour frontbench has called for fresh elections in Venezuela but has not called for Guaidó to be recognised as interim president.

The Spanish government has called for the immediate release of four members of a news team from the Spanish news agency EFE who have been detained in Venezuela.

EFE said three of its journalists – a Spaniard and two Colombians – and their Venezuelan driver were arrested by the intelligence service in Caracas on Wednesday.

According to the agency, the trio had travelled from Bogotá in Colombia to report on the crisis in Venezuela.

“Since learning of the arrest, the government, through our embassy in Caracas, is doing everything necessary to secure their swift release,” the Spanish government said on Thursday morning.

“The government demands that the relevant authorities release them at once. The government also urges the Venezuelan authorities to respect the rule of law, human rights and basic freedoms, of which the freedom of the press is a central element.”