COLOMBO, Sri Lanka — More evidence emerged Monday that the Sri Lankan government had ignored detailed warnings about an imminent terrorist attack, days before suicide bombers killed more than 250 people at crowded churches and hotels.

In a memo dated April 9 and labeled “Top Secret, (Eyes Only),” the chief of national intelligence warned the country’s police chief that “Sri Lanka based Zahran Hashmi of National Thowheeth Jama’ath and his associates are planning to carry out a suicide terrorist attack in Sri Lanka shortly.” The bombings came 12 days later.

The memo, whose authenticity was confirmed by two high-ranking government officials, is the earliest one revealed so far to have so obviously conveyed a sense of urgency. A security memo two days later warned of “a possible suicide attack” by the radical Islamist group but did not say when it was expected.

Day by day, the paper trail of detailed warnings gets longer, casting more doubts on President Maithripala Sirisena’s claims that he did not know the attack was coming.