Chinese police investigating two deadly bus explosions in a southwestern city have not found any links between the blasts and next month's Olympic Games, officials said Tuesday.

The explosions Monday on two public buses in Kunming, the capital of Yunnan province, had heightened fears of terrorism with less than three weeks to go before the opening of the Beijing games.

"We have not found evidence that links it to the Beijing Olympics but we continue to make efforts to find out the truth," Chinese Foreign Ministry spokesman Liu Jianchao said.

Two people were killed and 14 wounded in the explosions on bus route 54, which police said were deliberately set. One blast shattered windows and tore a gaping hole in the side of the bus.

Kunming police chief Du Min said investigators did not know whether the blasts were perpetrated by many people, or an individual, the official Xinhua News Agency reported.

He ruled out links to the Olympics and to disgruntled farmers in the province who clashed with police over the weekend.

The state-run Southern Metropolis Daily in Guangdong province reported Tuesday that police were checking into text messages allegedly sent to Kunming residents warning them to avoid buses just hours before the two explosions.

"(I) hope citizens receiving this message will not take bus routes 54, 64 and 84 tomorrow morning," the newspaper quoted the message as saying.

The text message also mentioned "ants," a slang term calling for the message be spread around. No further details were known.

Du denied that there was such a text message, Xinhua reported, calling it a rumor.

Authorities were offering a cash reward of $14,650 for information that can help solve the case.

The government has boosted national security to ensure a worry-free Olympics, which they say is a target for terrorism. The measures include stricter checks at subway stations and airports, and an anti-terror force of nearly 100,000 commandos, police and troops.

Most experts say the actual threat to the Beijing Games from terrorism is low, although the event has become a magnet for critics of the government.

Kunming is the capital of Yunnan province, 1,300 miles southwest of Beijing, and not generally considered a restive area.