A car explosion killed at least 10 people near a metro station at the landmark Red Fort monument in Delhi, India, on Monday.

More than 30 other people were “badly injured” in the blast, said Dr. Manish Kumar Jha, a physician at the local Lok Nayak Hospital. “Many are not in a position of recovering,” he told reporters.

While the cause of the blast is not yet known, airports, railway stations, government buildings and heritage sites across the country have been put on high alert, according to the Central Industrial Security Force. The US embassy in New Delhi is advising Americans to avoid the surrounding area as well as large crowds.

The Red Fort, known in India as the Lal Qila, is a 17th-century Mughal-era fort named for its large, red sandstone enclosing walls. The UNESCO World Heritage site is visited by millions of people throughout the year.

In a major breakthrough against terror networks operating, the Jammu and Kashmir Police, in coordination with Haryana Police, on Monday uncovered a large cache of explosives and arms from an apartment in Haryana’s Faridabad. Officials confirmed that 360 kg of suspected ammonium nitrate, along with 2,900 kg of IED-making material, including chemicals, detonators, wires, and other bomb-making components, were seized.

Two persons — Dr Muzammil Ahmad Ganaie, an assistant professor at Al-Falah University, Faridabad, and Dr Adil Ahmad Rather, a doctor from Pulwama — were arrested in connection with the seizure.