Turkey on Monday said it had summoned the US charge d'affaires in Ankara to demand an explanation over a leak by Edward Snowden that Washington has spied intensively on Turkish leaders since 2006.
Der Spiegel reported that as well as sharing intelligence with NATO partner Turkey, the United States and its ally Britain have been conducting extensive electronic surveillance on the Turkish leadership.
The German weekly said that the information was based on documents released by the fugitive former National Security Agency (NSA) operative Snowden, who has taken refuge in Russia.
It claimed the NSA placed "Turkey at the level of Venezuela, and even ahead of Cuba, in terms of US interest in intelligence collection".
Turkey's Deputy Prime Minister Bulent Arinc told reporters in Ankara that "the US charge d'affaires has been summoned to the foreign ministry and an explanation demanded."
The new US ambassador to Turkey, John Bass, is yet to arrive in Ankara.
The Turkish foreign ministry said in a statement after the meeting that it had asked the US authorities to provide a satisfactory explanation for the "grave allegations".
"If the allegations are true, it is obvious that these activities cannot be accepted and do not comply with the friendship between the two countries."
"The United States is expected to investigate the said allegations, and if they are true, terminate its activities targeting our state institutions and foreign missions."
President Recep Tayyip Erdogan, who last week switched from the job of premier which he held for over a decade, said he would be discussing the claims at the NATO summit in Wales and UN general assembly this month.
"All countries with established intelligence services do it all the time, but how they do it and what they reveal is important," he said before leaving on a foreign trip.
- 'Hourly reports on Kurds' -
Der Spiegel said the NSA began a major surveillance operation in 2006 aimed at hacking into the computers of Turkey's leadership.
The aim was to glean information about the strategic intentions of the Turkish leadership under Erdogan.
It said that the United States also spied on Turkey's embassy in Washington and its mission at the United Nations in New York.
The information was shared with the key intelligence partners of the United States -- Britain, Canada, Australia and New Zealand.
Der Spiegel said Britain had already developed its own operations in Turkey, with its GCHQ surveillance agency eavesdropping on political targets in the country.
Turkey has already expressed anger over a previous report in Der Spiegel that Germany had been spying on its NATO ally for years.
But Der Spiegel also said that at the same time there had been very tight cooperation between the United States and Turkey on sharing intelligence, particularly on Kurdish militants waging an insurgency in Turkey's southeast.
It said that the US had been able to keep Turkey informed of the location of Kurdish militant leaders on an hourly basis by tracking their mobile phones.
Der Spiegel also said that the false intelligence that prompted a Turkish airstrike in December 2011 that killed 34 suspected PKK militants -- who later turned out to be cigarette smugglers -- came from a US drone flight.
It said that one NSA document bluntly described Turkey as both a "partner and a target".