Gunmen killed an anti-government activist and wounded two others in the Thai capital on Saturday while protesters elsewhere blocked candidates from registering in upcoming elections, deepening a political crisis that threatens to derail democracy in this Southeast Asian nation.

The registration was suspended in four of the country's 77 constituencies. All are in the south, a sign of the limited national appeal the protest movement seeking to oust Prime Minister Yingluck Shinawatra enjoys outside of Bangkok.

The events followed comments Friday by the powerful army chief in which he declined to rule out the possibility of a coup in the country, which is a major U.S. ally, Southeast Asia's second largest economy and a popular tourist destination.

The long-running dispute between Thailand's bitterly divided political factions flared anew in November after Yingluck's elected government tried to introduce an amnesty for her brother, former Prime Minister Thaksin Shinawatra, to enable him to return to Thailand and escape a jail term for corruption.

Yingluck called early elections as a way of diffusing the crisis, but the protesters are demanding she resign and hand over power to an unelected council to carry out reforms. They are trying to disrupt the polls, which most people believe will give her a strong mandate thanks to strong support in the north and northeast of the country.

On Thursday, protesters tried to overrun a Bangkok sports stadium where election candidates were gathering to draw lots for their positions on ballots. Masked protesters fired rocks from slingshots as they tried to break into the building to halt the process, while police responded with tear gas and rubber bullets. Two people, including a police officer, were shot dead.

The overnight attack took place close to a protest camp in the city center, according to a government-run Erawan medical center. It said a 31-year man was killed by gunfire and two others wounded in the attack on Saturday at around 3:30 a.m. Local media said unidentified gunmen opened fire on guards close to a protest camp before escaping into the night.

Hundreds of candidates Saturday were registering for the polls.

But in four southern provinces, the process was stopped because protesters blocked the venues and local election officials wanted to avoid violence, said Puchong Nutrawong, secretary general of the election commission. Registration continued in a fifth province — Surat Thani — despite protests there, he said.

"Our policy is to avoid any confrontation," Puchong said.

Thailand's army has so far stayed out of the crisis, but it has staged 11 successful coups in the country's history — the last against then Prime Minister Thaksin in 2006 — so its intentions are being watched carefully.

Asked whether a military takeover was possible, army chief Gen. Prayuth Chan-ocha said simply, "That door is neither open nor closed ... it will be determined by the situation." While ambiguous, his words were taken by some as warning that it might one day intervene.

Thailand's political turmoil has its roots in the 2006 coup and the divisive rule of Thaksin, a former police officer who was accused of massive corruption during his six-years in power. In broad terms, the conflict pits the Thai elite and the educated middle-class against Thaksin's power base in the countryside, which benefited from his populist policies designed to win over the rural poor.

The protesters accuse Yingluck of being a proxy for Thaksin, who lives in self-imposed exile to avoid jail time for a corruption conviction but still wields influence in the country. An ill-advised bid by Yingluck's ruling Pheu Thai party to push an amnesty law through Parliament that would have allowed Thaksin's return from exile sparked the latest wave of protests.