Updated at 4:50 p.m. ET

Thai officials are downplaying the possibility that a foreign terrorist group is behind the bombing in central Bangkok this week that killed at least 20 people, including foreign tourists, and wounded dozens of others.

Police also appear to have ruled out a man in a yellow T-shirt seen on a CCTV video leaving behind a backpack moments before the blast at the Erawan shrine as well as another man suspected of being an accomplice.

The Associated Press reports that the two have been cleared "after one of them turned himself in and said he was a tour guide and the other was a Chinese tourist."

National police spokesman Lt. Gen. Prawut Thavornsiri said the two men "definitely" are no longer suspects, according to AP.

Earlier, a government spokesman said it was "highly unlikely" that a foreign network was behind Monday's attack, nor did he believe that Chinese tourists were the targets.

The Erawan shrine is popular with visiting Chinese. Three Chinese nationals were killed in the blast and 15 others were wounded.

Predominantly Buddhist Thailand has experienced a long-running Islamist insurgency in the country's south, where there is a Muslim majority. Several bombings have occurred there over the years.

But army chief Udomdej Sitabutr said on television Wednesday that the attack "does not match with incidents in southern Thailand [and] the type of bomb used is also not in keeping with the south."

Although authorities appear to have ruled out foreign terrorism, an arrest warrant for a man seen in a CCTV video leaving a backpack at the blast site moments before the explosion described him as an "unnamed foreigner" and accused him of a conspiracy to commit "premeditated murder" and weapons offenses.

"He didn't do it alone for sure," national police chief Somyot Poompanmoung was quoted by The Associated Press as saying.

"It's a network," he added, saying he was certain that Thai citizens were involved in the bombing.

Prime Minister Prayuth Chan-ocha appears to be pointing the finger of blame in the direction of the political opposition, which supports former Prime Ministers Thaksin Shinawatra and his sister Yingluck. Both leaders were ousted in military coups, the second of the two led by Prayuth, a former army chief.

Speaking on television Tuesday evening, Prayuth said the attack shows that Thailand "still has a person or a group of people with hostility to the nation operating actively," according to a translation published in the English-language Bangkok Post.

"They may be doing it for a political motive or to undermine the economy or tourism or for other reasons," he said.

Prayuth told reporters that the man must have been hired to plant the bomb. In the past, the government has accused Thaksin, a former telecom tycoon now living in exile, of paying political activists to stir up opposition to the country's military government.

However, as Michael Sullivan reported for NPR earlier this week, independent analysts cast doubt on the notion that the bombing was carried out by so-called Red Shirt partisans.

Meanwhile, the BBC reports that reporters found shrapnel near the scene of the blast today, calling into question the thoroughness of the investigation. Correspondent Jonathan Head reports that when he tried to bring the pieces to Bangkok police headquarters, he was turned away at the gate by officers who said the facility was closed.

Prayuth, who overthrew an elected government last year, was quoted today in The Bangkok Post suggesting that police working the case ought to watch the American police television drama Blue Bloods to get a better handle on investigative techniques.

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