The NSA surveillance whistleblower Edward Snowden has said US officials are waging a campaign to prevent him from taking up asylum offers as he called a meeting in Moscow airport with human rights groups.

In a letter sent to groups including Human Rights Watch and Amnesty International, the former intelligence agency contractor claimed there was "an unlawful campaign by officials in the US government to deny my right to seek and enjoy … asylum under article 14 of the Universal Declaration of Human Rights" and invited them to meet him at 5pm local time.

"The scale of threatening behaviour is without precedent: never before in history have states conspired to force to the ground a sovereign president's plane to effect a search for a political refugee," he wrote to the groups. "This dangerous escalation represents a threat not just to the dignity of Latin America or my own personal security, but to the basic right shared by every living person to live free from persecution."

Reuters quoted an airport official as saying Snowden would meet the groups on Friday afternoon in the transit area of Sheremetyevo, where he has remained since flying to Russia from Hong Kong on 23 June.

The 30-year-old former NSA employee is trying to negotiate asylum elsewhere to avoid facing charges in the US, including espionage, for divulging details about US electronic surveillance programmes.

"I can confirm that such a meeting will take place," an airport spokeswoman said.

Reuters said Amnesty and Transparency International had been invited to meet Snowden, with the former confirming it would attend.

Sergei Nikitin, the head of Amnesty International Russia, said: "Yes, I have received a brief email. It said that he would like to meet with a representative of a human rights organisation – there was not much information there. I'm planning to go."

Tanya Lokshina of Human Rights Watch confirmed she had been invited to the meeting and posted Snowden's letter on Facebook.

Snowden is still believed to be weighing up his options. Late on Thursday, Venezuela's foreign minister said the country had yet to receive a formal response to its offer of asylum.

"We communicated last week. We made an offer and so far we haven't received a reply," Elias Jaua told Reuters during a regional foreign ministers' meeting in Uruguay.

Venezuela is one of three countries to offer asylum to Snowden, along with Bolivia and Nicaragua.

In a separate email to Reuters, Snowden confirmed that the meeting with human rights groups would go ahead but said it would be closed to the press. He said he planned to speak to the media later.

The letter told the groups to bring identification and meet at 4.30pm at Sheremetyevo airport in Terminal F, "in the centre of the arrival hall [where] someone from airport staff will be waiting there to receive you with a sign labelled G9".

This article originally appeared on guardian.co.uk