KIGALI (Reuters) - Rwanda has asked a human rights researcher to leave the country, citing anomalies in her visa application, in a move the watchdog says is part of a crackdown on freedom of expression ahead of August's presidential election.

A Human Right Watch (HRW) statement on Saturday said Carina Tertsakian, its senior researcher in Rwanda, was told by immigration officials that she would not be granted a work visa.

"The immigration officials refused to put their decision in writing. They told Tertsakian that as a British national she could not exceed her 90-day legal stay in the country, which expires on April 24," the statement said.

"They alleged that there were anomalies in her visa application, specifically signatures and dates on the documents she had submitted."

Kigali's immigration department said the 90 days were for Tertsakian to address issues in her documents but they were now over.

"We were not satisfied by the explanations they gave us on the signatures. They claim that the signatures are genuine, much as we showed them the differences and they acknowledged them, so we asked her to leave," said Innocent Niyonsenga, a communications official at the immigration office.

HRW has been in Rwanda since before the 1994 genocide that killed 800,000 people.

In the last few weeks, the Rwandan government has said it was concerned about the work of rights organisations and senior officials have singled out HRW as being particularly insensitive about some of the factors that led to the genocide.

Georgette Gagnon, Africa director at HRW, told Reuters the refusal to grant a work permit was part of a crack down on freedom of expression ahead of the presidential election.

"In the last few weeks, we have seen repeated intimidation, harassment and obstruction of opposition parties, journalists and civil society in Rwanda.

"These developments take place against a backdrop of increasing intolerance of dissent and criticism in the run-up to presidential elections in August," she said.

"We are planning to appeal this decision and to continue with our work on human rights issues in Rwanda," Gagnon said.

HRW said Rwandan officials had not made any attempt to contact its headquarters or the individuals whose signatures they had queried.

Human rights groups have criticised Rwanda for planning the election without a meaningful opposition to President Paul Kagame's ruling Rwanda Patriotic Front. Emerging opposition groups say they face harassment, intimidation and legal and administrative barriers to registration .