By Jethro Mullen
Russian police have detained dozens of people in an anti-terrorism operation in Volgograd, the southern city where two suspected suicide bombings killed more than 30 people this week.
The heightened security measures, in which thousands of police officers searched hundreds of people, came as Australia announced limits on the movements of its athletes when they travel to Russia for the 2014 Olympic Games.
The death toll from the attacks has increased to 34 after some of those who were wounded succumbed to their injuries, state media reported.
The two deadly blasts in Volgograd have intensified fears over the danger of terrorism in Russia following a threat earlier this year from a Chechen extremist group to use "maximum force" to disrupt the Games, which will take place in the southern city of Sochi in February.
No group has so far claimed responsibility for carrying out the suspected bombings in Volgograd.
Australia said Tuesday that none of its athletes competing in the Olympics will travel to Sochi using ground transportation in Russia -- they will only travel by air.
Australian athletes will only train and compete in Sochi and won't vacation elsewhere in Russia after the Games, said John Coates, the president of the Australian Olympic Committee.
"Families of athletes and all other participants of the Olympic Games, including media and spectators, should note the steps we are taking for the safety and welfare of our athletes," Coates said in a statement on the committee's website.
He nonetheless echoed comments from the International Olympic Committee expressing confidence that Russian authorities will do everything "to ensure the security of the athletes and all of the participants of the Olympic Games."
Key transit point
While security in Sochi and its surrounding area is considered to be very tight, the attacks in Volgograd, a major transportation hub for southern Russia, have raised concerns about the potential vulnerability of other areas of the country.
Volgograd is a main transit point for people traveling by train to Sochi, which is situated just over 400 miles (645 kilometers) to the southwest.
The number of people killed in an explosion at the Volgograd's main rail station Sunday now stands at 18, the state-run news agency RIA Novosti reported Tuesday, citing the Emergencies Ministry.
The toll from a blast on a trolleybus during the morning rush hour Monday has reached 16, the agency said, attributing the information to health officials.
Russian authorities have described both explosions as terrorist attacks and vowed to continue their "tough and consistent offensive" against extremists.
About 5,200 police officers are now on the ground in Volgograd for an anti-terrorism operation, Andrei Pilipchuk, a regional police official, said on Russian television.
Police are checking people's documents in all crowded areas of the city and have so far detained 87 people who put up resistance or didn't have documents allowing them to carry weapons, Pilipchuk said.
But it wasn't clear if any of those held had any suspected connection to the attacks or would face any charges.
A total of 1,500 buildings have been "examined" and more than 1,000 people have been searched in the operation, Pilipchuk said.
U.S. offers support
The United States has offered its "full support to the Russian government in security preparations for the Sochi Olympic Games," National Security Council spokeswoman Caitlin Hayden said in a statement Monday.
"We would welcome the opportunity for closer cooperation for the safety of the athletes, spectators, and other participants," Hayden said.
The U.S. State Department said American citizens planning to attend the Games should "be reminded that threats have been made against the Olympic Games and acts of terrorism, including bombings, continue to occur in Russia."
"This is an exciting, positive, happy international sporting event, but people going there do need to maintain vigilance and watch out for their own security and safety," Marie Harf, a State Department spokeswoman said at a regular briefing Monday.
Harf said the department was "very focused" on the security situation in Russia, but she declined to say whether any additional measures had been taken since the Volgograd bombings.
CNN's Diana Magnay and Arkady Irshenko contributed to this report.
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