Sudanese warplanes bombed a South Sudanese town Monday morning, ignoring international calls to stop the attacks and ratcheting up the threat of a full-blown war between the two nations.

According to the United Nations mission in South Sudan’s capital, Juba, the bombings in the heavily populated border town of Bentiu began at 8:30 a.m., striking a market on its outskirts and killing two civilians, including a child. Ten people were wounded. Reporters at the scene described seeing the boy’s body in the marketplace.

“These indiscriminate bombings resulting in the loss of civilian lives must stop,” said Hilde F. Johnson, the top U.N. official in South Sudan.

U.N. Secretary General Ban Ki-moon condemned Sudan’s bombardment of the town and urged the government in Khartoum to “cease all hostilities immediately,” according to a statement from his office.

“The secretary general reiterates that there can be no military solution to the disputes between Sudan and South Sudan,” the statement said.

(By Laris Karklis/The Washington Post/The Washington Post)

When asked at a news conference what the U.N. mission could do to stop Sudan from bombing civilian targets, Johnson said any stronger measures were not in the mission’s hands. “It is totally in the hands of the U.N. Security Council,” she said.

The attack Monday came hours after Sudanese forces launched an incursion more than six miles inside South Sudan’s border — and three days after South Sudan ordered a withdrawal of its troops from the contested oil town of Heglig to give international diplomacy a chance to solve the disagreements between the nations.

Sudan denied any attack inside the South Sudanese border. It instead asserted that it had repulsed a major attack by southern-backed rebels in South Kordofan, on its side of the border.

But there appeared to be little doubt that Monday’s bombing was conducted by the government in Khartoum. Witnesses reported seeing Soviet-made warplanes attacking Bentiu. The South Sudanese military does not have an air force.

Maj. Gen. Mac Paul, deputy director of military intelligence for South Sudan, said two MiG-29 fighters dropped three bombs. He said two of them landed near a bridge that connects Bentiu, the capital of Unity state, and Rubkona, the market that was attacked, according to the Associated Press. Paul said the other bomb exploded in Rubkona.

“The bombing amounts to a declaration of war,” Paul said.

Violence has steadily increased since South Sudan broke away from Sudan in July, becoming the world’s newest country. Khartoum and Juba have been embroiled in disagreements over border areas and the sharing of oil revenue. They have backed proxy rebel forces inside each other’s borders and have engaged in high-stakes verbal assaults that have drawn them closer to war.

The United States and other members of the international community have urged both sides to stop their attacks. The latest such call came from President Obama, who on Friday urged the presidents of both countries to return to the negotiating table to resolve their disputes.

But tensions continue to rise. On Saturday night in Khartoum, mobs of Muslims razed a Catholic church frequented by South Sudanese, apparently in retaliation for the South Sudanese takeover of Heglig, which both sides claim as their territory. South Sudan said it withdrew from the area, but Khartoum says its troops pushed the South Sudanese out, once again inflaming animosities.

“We are building up troops because we think that the Sudanese army is also building up,” Paul told reporters in Bentiu on Sunday.

On Monday, Sudanese President Omar Hassan al-Bashir visited troops near the Heglig oil field and ruled out talks with South Sudan because of its takeover of the town.

“We will not negotiate with the South’s government, because they don’t understand anything but the language of the gun and ammunition,” he told Sudanese troops, according to Reuters.

Staff writer Colum Lynch at the United Nations contributed to this report.