Nasser Judeh, the Jordanian government spokesman, said the visit by Mahmoud al-Zahar, which was planned for Wednesday, had been "put off until further notice".

He said "missiles, explosives and automatic weapons were seized in the last couple of days", but declined to say whether anyone had been arrested.

Hamas spokesman Osama Hamadan declined to comment on Judeh's remarks, saying late on Tuesday that he had not seen the Jordanian statement.

Government officials said privately that al-Zahar, the most senior Hamas leader in the Gaza Strip, had asked to visit Jordan to meet Abdul-Illah al-Khatib, the foreign minister.

They said they did not know what al-Zahar planned to discuss or whether he would have requested financial aid.

Exploring potential targets

In a separate statement to the official Petra news agency, Judeh said Jordanian security services had observed Hamas members "exploring several vital [potential] targets" in the capital, Amman, and other cities.

"The Jordanian government considers such practices in contradiction with the essence of Jordanian-Palestinian relations," Judeh said.

"Hamas is using two languages in dealing with Jordan," he added.

Jordan, which signed a peace treaty with Israel in 1994, maintains a tough line on militants and once expelled the current leader of Hamas, Khaled Mishaal, for his activities.