* Two-year Security Council term to begin on Jan. 1
* Lithuania topped the vote tally, winning 187 ballots (Adds quotes, background and details)
UNITED NATIONS, Oct 17 (Reuters) - Saudi Arabia, Chad and Nigeria were elected by the U.N. General Assembly on Thursday to serve a two-year term on the U.N. Security Council as human rights groups called for all three countries to improve their records.
Chile and Lithuania also won seats on the 15-member council. There are five veto-wielding permanent council members - the United States, Britain, France, Russia and China - and 10 temporary members without veto power.
The group elected on Thursday will replace Azerbaijan, Guatemala, Pakistan, Morocco and Togo on the Security Council on Jan. 1, 2014. They were unopposed, but had to obtain approval from two-thirds of the 193-member General Assembly.
Of the 191 U.N. members who voted, Lithuania won 187 votes, Chile and Nigeria each picked up 186 votes, Chad secured 184 votes and Saudi Arabia 176 votes.
"Security Council members are routinely called upon to address critical human rights and humanitarian issues," said Hillel Neuer, executive director of U.N. Watch, a Geneva-based advocacy group that monitors the United Nations. "Saudi Arabia and Chad have abysmal records on human rights."
Saudi Arabia, a patriarchal society that applies an austere version of Sunni Islam, has repeatedly been slammed for its record on women's rights. Last month it topped a World Bank list of countries with laws that limit women's economic potential.
Saudi Arabia, which is also campaigning to be elected to the U.N. Human Rights Council, grants fathers guardianship over their daughters, giving them control over who they can marry and when, and it is also the only country in the world where women are barred from driving.
Human Rights Watch said taking up these prominent U.N. positions should spur Riyadh to "clean up its act."
A senior Security Council diplomat, speaking on condition of anonymity, welcomed the election of a key Middle East country as the world attempts to bring to an end a 2-1/2-year-old civil war in Syria that has killed more than 100,000.
"Our election today is a reflection of a long-standing policy in support of moderation and in support of resolving disputes in peaceful means," said Saudi Arabia's U.N. ambassador, Abdullah Al-Mouallimi, after the vote.
Al-Mouallimi told reporters that Saudi Arabia supported the Syrian struggle for "freedom and prosperity and unity." "We look forward to working with the rest of the international community to help our Syrian brothers achieve their objectives," he said.
Chad was named in a U.N. report in June for recruitment of child soldiers. The report said that while progress had been made and the army has a policy of not recruiting children, there were still dozens of verified cases.
"Chad's election while listed on the U.N. list of shame of countries that use child soldiers should be another incentive for the authorities to end a backward practice that the Security Council has spent a great deal of time working against," said Human Rights Watch U.N. Director Philippe Bolopion.
Bolopion also said Nigeria "should lead by example and end chronic impunity for abuses by its security forces as well as protect civilians from Boko Haram's horrific violence."
A Nigerian government rights watchdog said in July it had credible reports the country's own forces carried out extra-judicial killings, torture, rape and arbitrary detention in efforts to quell Boko Haram, an Islamist sect that has killed thousands in a campaign to revive an ancient Islamic caliphate in Nigeria's northeast.
In May the Nigerian military began its most concerted effort yet to end the 4-year-old Islamist insurgency.
Nigerian Foreign Minister Viola Onwuliri told reporters after the Security Council vote: "We assure that Nigeria will not disappoint anybody."