BUFFETED by financial squalls and fearful of a Libyan-like upheaval, Sudan's president, Omar al-Bashir, is digging in hard. He is hammering groups opposed to his National Congress Party, while using his army and rebel proxies to bait South Sudan, his diminished country's newly independent neighbour. Fighting in the south's Unity state, close to the border, has left scores dead. A lot more have died in South Kordofan, a state within his rump Sudan, just north of the new border, where ethnic Nuba are pressing for control of a mountain range.

Mr Bashir is wanted by the International Criminal Court in The Hague for crimes against humanity in Darfur, his country's ravaged western province. Some of his genocidal generals are still in operation. One of them probably gave the order to bomb a refugee camp in South Sudan on November 10th. According to eyewitnesses, bombs were pushed out of the back of an Antonov transport plane—a signature method of Sudanese air raids in the past.

America has urged South Sudan to have “the wisdom and restraint not to take the bait”. President Salva Kiir accused the north of stoking war and infiltrating saboteurs into his country. At the same time, he has exploited the heightened tension to silence critics at home. His government has the moral high ground for the moment, but claims by Mr Bashir that it is backing his enemies are hard to disprove. South Sudanese people who have chosen to stay in the north, despite their homeland's independence in July, may be vulnerable to retribution.

The new country is a brittle construct. Power-sharing across tribal lines is shaky. Military and oil interests are dominated by one ethnic group, the Dinka, themselves riven by differences. Others are disgruntled—and armed.