Uber is ramping up driver background checks and other security measures worldwide after the smartphone-focused car-sharing service was banned in New Delhi following the alleged rape of a passenger.

The incident earlier this month in the Indian capital was one of a string of setbacks for the popular but controversial San Francisco-based start-up -- valued at $40 billion -- which lets customers hail and pay for taxis or private vehicles via a smartphone app.

"We believe deeply that, alongside our driver partners, we have built the safest transportation option in 260 cities around the world," Uber head of global safety Philip Cardenas said Wednesday in a blog post.

"But we have more work to do, and we will do it."

Uber, which says it tracks every journey by GPS, is developing a safety "roadmap" that includes voice recognition to verify drivers' identities and providing ways for riders to instantly contact the company or loved ones in emergencies.

Uber goes by local regulations when doing background checks of drivers, but is working on making the system better in places where the checks are tricky or untenable.

"This is of deep concern to us," said Cardenas.

"We are finding solutions in many places that range from polygraph exams that fill gaps in available data to adding our own processes on top of existing screening for commercial licenses -- which is what we are undertaking in India."

- 'Multi-layered checks' -

Uber's website describes a "rigorous" background check process developed in the United States and applied to all of its ridesharing partners.

The process was said to include checks of motor vehicle department and criminal justice records, where available.

"Across the US and in dozens of countries around the world Uber conducts thorough, multi-layered background checks that have resulted in tens of thousands of potential drivers being denied the opportunity to partner on the Uber platform," Cardenas said.

Every Uber ride is traced by location-tracking satellites, and application software displays a designated driver's picture, license plate number and vehicle type to the person waiting to be picked up.

Uber also promised steps to improve customer support, including responses to trouble.

New Delhi last week extended a ban on Uber to all web-based taxi services in the Indian capital.

The city government announced that it was banning Uber with immediate effect after a young female passenger accused the driver of raping her.

Indian police said Uber did not conduct a background check on the driver, who was working for the company while on bail on multiple charges including assault, robbery and rape.

Uber's rapid growth has caused tensions, especially with rival taxi companies which protest that Uber cars are not subject to the same regulations.

Uber has provided 140 million rides for people this year, according to Cardenas.

The company launched in early 2009 and set up its India operation in September of last year.

Along with being targeted by established taxi operators in many cities and ruled illegal in some jurisdictions, the company has seen its image tarnished by executives' gaffes and concerns on privacy.

- China move -

Chinese search engine Baidu, the country's equivalent of Google, announced Wednesday it has bought a stake in Uber for an undisclosed sum.

Baidu will also link users of its mapping and search functions with Uber drivers, the two companies announced at a ceremony in Beijing. The investment has previously been reported to be as much as $600 million, according to state-run China National Radio.

"Our efforts here in China are unique and will continue to be, let's call it, more unique than anywhere else," Uber CEO Travis Kalanick said at a press conference after the signing ceremony.

"You have to do things differently here in China," he said, without elaborating.

Uber, which connects riders and local drivers, currently operates in nine cities across China, including the capital Beijing and financial hub Shanghai.

But its presence is dwarfed by China's two dominant taxi-hailing apps -- Kuaidi Dache, in which e-commerce behemoth Alibaba has a stake, and Didi Dache, backed by technology giant Tencent.