* UN Council extends mandate of special rapporteur
* China, Russia vote against motion brought by Sweden
* Iran says rights concern a pretext for undue pressure
GENEVA, March 22 The United Nations renewed the mandate of its human rights investigator for Iran on Thursday, but Russia and China voted against the resolution that expressed "serious concerns" about a country said to have the highest per capita execution rate in the world.
As Western nations tighten sanctions on Iran over its nuclear programme, Thursday's vote at the U.N. Human Rights Council added to the pressure by extending the one-year term of the investigator who has been denied entry by Tehran.
Just as they opposed the economically crushing U.S. and EU sanctions on Iran and twice vetoed Security Council resolutions against Syria, Russia and China were among the five countries that voted against the human rights resolution that was backed by 22 countries with 20 abstentions.
The vote means that former Maldives Foreign Minister Ahmed Shaheed retains for another year the role of looking into human rights in the Islamic Republic.
After his first year in the job he issued a report earlier this month showing a rapidly increasing rate of executions in Iran, with some 670 people put to death last year, most of them for drug crimes that do not merit punishment under international law and more than 20 for offences against Islam.
According to rights group Amnesty International, only China, with a much bigger population, executes more people.
Shaheed also voiced concern about the abuse of minorities and the persecution of homosexuals and labour unions.
The delegate for Sweden, which sponsored the resolution, urged Tehran to work with the investigator, an unlikely prospect as Iran says his appointment was merely part of the West's manoeuvres against it.
"The deteriorating situation of human rights in the Islamic Republic of Iran continues to be of great concern. We regret that the special rapporteur, Dr. Shaheed, has not been given access to the country," Sweden's diplomat, Irina Schoulgin Nyoni, told the meeting.
"We strongly encourage the Iranian authorities to engage in dialogue and cooperation with this important mechanism of the Human Rights Council," she added.
Sayed Mohammad Reza Sajjadi, Iran's ambassador to the United Nations in Geneva, said human rights were being used as a pretext to advance the political interests of specific states. (Reporting by Stephanie Nebehay; Editing by Robin Pomeroy)