BISSAU, Guinea-Bissau — One day after the military in this tiny West African nation shelled a presidential candidate's home and sealed this capital city from outsiders, it was still unclear Friday who, exactly, was in charge.

The military announced Friday night that it had arrested Carlos Gomes Jr., a former prime minister and a leading presidential candidate, as well as interim President Raimundo Pereira. But no new successor has been proclaimed, and the reasons for the coup remained opaque.

There was speculation that Gomes could have run afoul of the military by promising to end a lucrative arrangement between the military and international drug traffickers. Analysts say the drug traffickers pay the military to look the other way — or even help out — as cocaine shipments are flown in by small planes from South America, stashed away in the country's coastal islands, and smuggled into Europe.

"The drugs are behind it all," said Jan Van Maanen, the honorary British consul in Guinea-Bissau. "It's a nice income for the army and they stand a chance of losing it all."

Analysts said, however, that the motive behind the coup here most likely was the same as for previous ones — Guinea-Bissau's military tends to oust politicians it doesn't like to make room for politicians it prefers.

"Guinea-Bissau has a long history of very specific kinds of coups where the army never assumes power but turns it over very quickly," said Vincent Foucher, a Dakar-based researcher with the International Crisis Group, a Brussels-based group that studies conflicts around the world. "Only a few people get killed each time."

That's different from the coup in nearby Mali three weeks ago, where an unknown army officer overthrew the country's democratically elected president and suspended the constitution ahead of April 29 elections, complaining that the civilian government had not done enough to stop a rebellion by nomadic tribesmen in the country's north. The coup plotters, however, surrendered their authority this week after West African neighbors shunned them and the Tuareg nomad rebels captured most of the country's northern reaches.

Analysts say that the recent turmoil in West Africa — including the Mali coup — isn't so much a sign of spreading regional instability as it is perhaps an indication of growing pains for budding democracies.

This year alone, almost a dozen West African countries have legislative or presidential elections scheduled. And as the era of strongmen phases out, elections begin to play a larger role in determining countries' futures, which can lead to increased tensions.

"Clearly, it's a really challenging time for the region," said Peter Thompson, the head of a British electoral observation team that has been sent to Guinea-Bissau.

Some elections have gone smoothly. In neighboring Senegal, for example, longtime President Abdoulaye Wade peacefully stepped down after losing a re-election bid last month.

In Guinea-Bissau, a first round of presidential elections had been held last month and the runoff was scheduled for April 29, with Gomes, who received 49 percent in the first round, expected to win.

Then came Thursday's coup. At 7:30 p.m. soldiers launched four or five grenades at Gomes' house, knocking out walls, according to Thompson, who heard the attack. Heavy gunfire followed for about an hour.